Geologic units in Vermont (state in United States)

Additional scientific data in this geographic area

Waits River Formation - carbonaceous phyllite and limestone member (Lower Devonian and Upper Silurian) at surface, covers 15 % of this area

Dark-gray to silvery-gray, lustrous, carbonaceous muscovite-biotite-quartz (±garnet) phyllite containing abundant beds of punky-brown-weathering, dark-bluish-gray micaceous quartz-rich limestone in beds ranging from 10 cm to 10 m thick. Part of the Connecticut Valley Trough.

Gile Mountain Formation - quartzite and metapelite member (Lower Devonian) at surface, covers 4 % of this area

Gray to light-gray, fine-grained micaceous quartzite a few centimeters to tens of centimeters thick, interbedded with dark-gray graphitic slate, phyllite, or schist. Part of the Connecticut Valley Trough.

Moretown Formation - “pinstriped” granofels member (Lower Ordovician to Cambrian?) at surface, covers 3 % of this area

Light-gray to pale-green, whitish-gray-weathering, chlorite-biotite-plagioclase-quartz granofels and tectonically “pinstriped” granofels and feldspathic biotite quartzite. Part of the metasedimentary host rocks of the North River Igneous Suite. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Hazens Notch Formation - undivided (Cambrian and Neoproterozoic) at surface, covers 3 % of this area

Schist, gneiss, and quartzite; dark-rusty-brown graphitic biotite-muscovite-chlorite-quartz (±garnet) schist and gneiss; black albite porphyroblasts, large euhedral pyrite, and beds of dark-gray foliated quartzite are common. Unit includes rusty-weathering schist without graphite and rocks identical to Fayston Formation. Cover rocks north of the Lincoln Mountain massif.

Biotite-quartz-plagioclase gneiss (Middle and Early Mesoproterozoic) at surface, covers 3 % of this area

A widespread, heterogeneous unit of well-layered, predominantly biotite-quartz-plagioclase gneisses containing variable amounts of magnetite, hornblende, and garnet, and little potash feldspar. Plagioclase-rich layers contain epidote-crowded plagioclase and isolated igneous quartz grains and probably are metadacitic volcanics and volcaniclastic rocks. Unit varies from very dark gray biotitic gneiss to light-gray more plagioclase- and quartz-rich gneiss, contains quartz-rich layers, minor amphibolites, rusty-weathering garnetiferous quartzites, and calc-silicates and marbles which locally are mappable. Association suggests an accumulation of volcaniclastic and clastic sediments. Areas of Y1,2bg associated with 1,400- to 1,350-Ma intrusive rocks range down into the Early Mesoproterozoic, whereas the upper parts may be Middle Mesoproterozoic. Rocks mapped as Y1,2bg may not all be correlative. Part of the aluminous schists and gneisses of the Washington Gneiss and Wilcox Formation and related rocks. Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Pinnacle Formation - undivided (Cambrian and Neoproterozoic) at surface, covers 3 % of this area

Gray, foliated muscovite-chlorite-biotite-feldspar-quartz schist, phyllite, and metagraywacke. Quartz is commonly blue, and local thin conglomeratic horizons are present. Feldspathic biotite phyllitic metawacke is interlayered with lenses of quartz, feldspar, and gneiss-pebble to -cobble conglomerate (CZpc). Cover rocks of the Lincoln Mountain massif and northwestern flank of the Green Mountain massif.

Ottauquechee Formation - carbonaceous phyllite member (Cambrian) at surface, covers 2 % of this area

Predominantly dark-gray to black, carbonaceous to highly graphitic, fine-grained sulfidic biotite-muscovite-quartz phyllite having silicic laminae. Includes black quartzites not mapped separately. Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks.

Albee Formation (Ordovician and Cambrian) at surface, covers 2 % of this area

Light-gray to greenish-gray, white-weathering, fine-grained feldspathic metasandstone and metasiltstone, and light-gray to greenish-gray to dark-gray phyllite. Lesser amounts of quartzite. Rare calc-silicate nodules. Generally sharply bedded, but graded beds as well as slump structures are locally obvious. Tourmaline is a sporadic accessory mineral. May be sulfidic (either pyrite or pyrrhotite) and rusty weathering. “Pinstriping” is common. U-Pb zircon SHRIMP age of 492.5±7.8 Ma from a porphyritic tonalite sill about 2 km east of West Bath, N.H. (D.W. Rankin, USGS, unpub. data, 2011). Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt.

Bull Formation - Mettawee slate facies (Neoproterozoic) at surface, covers 2 % of this area

Predominantly greenish-gray to pale-lustrous-green chlorite-muscovite-quartz phyllite; and green and purple, bedded and mottled phyllite. Locally contains boudins and thin beds of limestone and pods of pinkish-gray to cream-white dolostone, and minor quartzite. Unit interfingers with the West Castleton Formation above and laterally grades into the Bomoseen Graywacke Member. Also shown as CZnm (Mettawee Member of the Nassau Formation of Potter, 1972). Rocks of the Giddings Brook, Sunset Lake, and Bird Mountain slices. Part of the Taconic Allochthon.

Gile Mountain Formation - thick-bedded micaceous feldspathic quartzite member (Lower Devonian) at surface, covers 2 % of this area

Brown to gray, noncarbonaceous quartz-mica schist and feldspathic quartzite in beds 50 cm to 5 m thick; gradational to Dgqs through interbedding of phyllite beds and decrease in thickness of quartzite beds. Part of the Connecticut Valley Trough.

Gile Mountain Formation - rhythmically graded member (Lower Devonian) at surface, covers 2 % of this area

Light- to medium-gray, fine-grained micaceous quartzite to dark-gray muscovite-quartz-biotite carbonaceous phyllite or schist in beds 10 to 25 cm thick; and dark-gray micaceous phyllite or schist containing beds of micaceous quartzite; locally thickly bedded. Detrital volcanic zircons yield a U-Pb age of 409±5 Ma, no. 51 (McWilliams and others, 2010). Part of the Connecticut Valley Trough.

Stowe Formation - schist and phyllite member (Cambrian and Neoproterozoic?) at surface, covers 2 % of this area

Predominantly fine-grained, lustrous, well-foliated, silvery-green, grayish-green, and bright-green, quartz-ribbed and -knotted, magnetite-chlorite (biotite)-albite (plagioclase)-sericite (muscovite)-quartz phyllite and schist. Locally richly garnetiferous and biotite-flecked schist (CZsgt) at higher grades. Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks.

Underhill Formation (Cambrian and Neoproterozoic) at surface, covers 2 % of this area

Silvery-green quartz-muscovite-chlorite schist and phyllite, commonly with albite and magnetite; locally contains dolomite. Cover rocks north of the Lincoln Mountain massif.

Cheshire Quartzite (Lower Cambrian) at surface, covers 2 % of this area

Light-gray- to tannish-gray-weathering, massive to poorly bedded vitreous quartzite. Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

Fairfield Pond Formation (Cambrian and Neoproterozoic) at surface, covers 2 % of this area

Light-gray to light-green, quartz-sericite-chlorite (±magnetite±biotite) phyllite and foliated quartzite. Cover rocks north of the Lincoln Mountain massif.

Dunham Dolostone (Lower Cambrian) at surface, covers 2 % of this area

Buff- and pink-mottled and massive, or light-gray, pinkish-gray-weathering, and massive to poorly bedded dolostone. Contains distinctive small pebbles and grains of well-rounded quartz; minor beds of dolostone-breccia and conglomerate occur near Rutland. Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

Stony Point Formation (Upper Ordovician) at surface, covers 2 % of this area

Dark-gray calcareous shale with beds of bluish-gray limestone. Rocks of the Laurentian Margin. Part of the Adirondack lowlands and Lake Champlain lowlands (west of the Orwell and Champlain thrusts). Also part of the Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

Fayston Formation - albite schist member (Lower Cambrian and Neoproterozoic) at surface, covers 2 % of this area

Silvery-green to grayish-green, medium-grained albite-chlorite-muscovite-quartz (±garnet±magnetite) schist with white albite porphyroblasts; resembles albitic schists of the Tyson Formation (CZtab) and green albitic granofels of the Hoosac Formation (CZhgab). Locally contains unmapped light-gray, thin quartzites; salt-and-pepper-colored, medium- to coarse-grained pyrite-magnetite-biotite-albite-quartz schist and gneiss; and silvery-dark-gray to rusty-weathering, medium-grained chlorite-tourmaline-albite-muscovite-quartz schist. The Fayston south of Mount Abraham is interca-lated with rocks of the Tyson Formation and with the schists of the Pinney Hollow Formation. Cover rocks north of the Lincoln Mountain massif.

Waits River Formation - slate and phyllite member (Lower Devonian and Upper Silurian) at surface, covers 1 % of this area

Predominantly dark- to light-gray, lustrous, carbonaceous chlorite-biotite-muscovite-quartz slate, phyllite, or schist; contains thin beds of quartzite and only sparse layers of punky-weathering limestone. Shown south of the Pomfret dome where rocks typical of the Gile Mountain Formation are absent, and near Randolph. Part of the Connecticut Valley Trough.

Averill pluton (Devonian) at surface, covers 1 % of this area

Gray to pink, medium- to coarse-grained garnet-muscovite-biotite granite and pegmatite, undifferentiated. Igneous rocks of the Northeast Kingdom batholith of Ayuso and Arth (1992). Part of the New Hampshire Plutonic Suite.

Pinney Hollow Formation - phyllite member (Cambrian and Neoproterozoic) at surface, covers 1 % of this area

Light-greenish-gray to lustrous pale-green chlorite-muscovite-quartz (±chloritoid±garnet±magnetite) phyllite. Unit is locally albitic and contains minor beds of quartzite. Cover rocks of Green Mountain anticlinorium.

Chipman Formation - Bascom Formation (Middle and Lower Ordovician) at surface, covers 1 % of this area

Interbedded orangey-tan- to buff-weathering dolostone and bluish-gray to gray mottled dolomitic limestone or calcite marble and calcareous sandstone. In southern Vermont east of the Taconic Range, rocks mapped as Bascom Formation may include unmapped members of the Chipman Formation. Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

Winooski Dolostone (Middle Cambrian) at surface, covers 1 % of this area

Well-bedded dolostone weathering beige, cream, and buff, with green, red, or gray phyllite, siliceous partings, and thin beds of blue-quartz-pebble conglomerate and quartzite. Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

Northfield Formation (Lower Devonian and Upper Silurian) at surface, covers 1 % of this area

Dark-gray to silvery-gray, lustrous, fine-grained carbonaceous quartz-muscovite phyllite and silicic phyllite, and garnet-rich biotite-muscovite-quartz schist; contains millimeter- to centimeter-thick beds of gray quartzite and metasiltstone, and thicker beds of quartz-feldspar grit or quartzite near base. Transition zone into Waits River Formation west of the Guilford dome consists of as much as 5 percent beds of punky limestone. Part of the Connecticut Valley Trough.

Quartz schist and gneiss (Middle Mesoproterozoic) at surface, covers 1.0 % of this area

Dark-tan- to rusty-tan-weathering, garnet-muscovite-biotite-quartz-plagioclase gneiss and rusty schist, locally containing abundant chloritized garnet; lustrous yellowish-grayish-green phyllonitic retrograde varieties contain chloritoid-chlorite and relict garnet (red dot overprint). Part of the aluminous schists and gneisses of the Washington Gneiss and Wilcox Formation and related rocks. Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Biotite-granitic gneiss (Middle Mesoproterozoic) at surface, covers 1.0 % of this area

A heterogeneous unit consisting of granitic and granodioritic and aplite biotitic microcline-rich gneisses, highly gneissic and locally migmatitic, occurring in the southern part of the Green Mountain massif. U-Pb zircon TIMS age of 1,221±4 Ma, no. 12 (Ratcliffe and others, 1991; Aleinikoff and others, 2011) obtained from Londonderry. Unit intrudes rocks of South Londonderry Igneous Suite. Stratton Mountain Intrusive Suite (Middle Mesoproterozoic) (1,244±8 Ma to 1,221±4 Ma). Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Iberville Formation (Upper Ordovician) at surface, covers 0.8 % of this area

Dark-gray shale with thin discontinuous beds of crossbedded and graded dolomitic siltstone. Rocks of the Laurentian Margin. Part of the Adirondack lowlands and Lake Champlain lowlands (west of the Orwell and Champlain thrusts).

Clarendon Springs Formation (Upper Cambrian) at surface, covers 0.8 % of this area

Steel-gray-weathering, light-gray, massive calcitic dolostone grading upward into darker, more fissile calcitic dolostone containing white quartz knots near top; unit locally brecciated. Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

Monkton Quartzite (Middle Cambrian) at surface, covers 0.8 % of this area

Reddish-brown, pebbly, thin- to thick-bedded sandstone, orangey-gray- and buff-weathering well-bedded dolostone, and reddish-brown-weathering dolomitic quartzite. Unit discontinuous in southern Vermont. Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

Netop Formation - chlorite phyllite member (Cambrian and Neoproterozoic) at surface, covers 0.7 % of this area

Light-green to gray, lustrous, chlorite±chloritoid-muscovite-quartz phyllite and greenish-gray metasiltstone. Rocks of the Dorset Mountain slice (includes Dorset Mountain proper and Mount Equinox, southward to West Mountain near Bennington). Part of the Taconic Allochthon.

Knox Mountain pluton (Devonian) at surface, covers 0.7 % of this area

Light-gray, medium-grained, quartz-rich biotite-muscovite granite. Has distinctly more potassium feldspar and is lighter gray than rocks of the East Barre plutons. Part of other plutons of the New Hampshire Plutonic Suite.

Shelburne Marble (Lower Ordovician) at surface, covers 0.7 % of this area

Predominantly light-gray- to white- and bluish-gray-streaked calcite marble and massive white- and green-streaked calcite marble. Locally contains intermediate dolostone and gray limestone beds. Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

Hoosac Formation - albite-quartz granofels member (Lower Cambrian and Neoproterozoic) at surface, covers 0.6 % of this area

Light-gray- to whitish-gray-weathering, massive to thickly bedded medium-grained biotite-white albite-quartz granofels; locally is a medium-gray, finer grained, more biotite-rich albitic quartz schist of gneissic aspect. Eastern flank of the Green Mountain massif and eastern domes.

Skeels Corners Slate (Lower Ordovician and Cambrian) at surface, covers 0.6 % of this area

Laminated black slate with thin orange dolostone beds; includes massive dolostones mapped as Saxe Brook Formation by others in the Highgate area. Cover rocks of the Saint Albans area.

Jay Peak Formation - schist member (Cambrian and Neoproterozoic) at surface, covers 0.6 % of this area

Light-grayish-green, fine-grained, chlorite-muscovite-quartz phyllite or schist and quartzite; white quartzofeldspathic layers alternate with green chloritic phyllitic layers; locally albitic. Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks.

Glens Falls Limestone (Upper Ordovician) at surface, covers 0.5 % of this area

Dark-bluish-gray-weathering, thinly bedded dark-gray to black granular limestone; locally grades upward into sooty- weathering shaly limestone beds rich in fragments of the trilobite Cryptolithus. Rocks of the Laurentian Margin. Part of the Adirondack lowlands and Lake Champlain lowlands (west of the Orwell and Champlain thrusts). Also part of the Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

Hortonville Formation - shale and phyllite (Upper Ordovician) at surface, covers 0.5 % of this area

Dark-gray siliceous shale and phyllite containing thin beds of bluish-gray argillaceous limestone and minor beds of gray to tan quartzite. Grades into limy shales of the Stony Point Formation. Unit mapped west of the Taconic allochthon, and northwest of the Sudbury slice. Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

Pinnacle Formation - metawacke member (Cambrian and Neoproterozoic) at surface, covers 0.5 % of this area

Gray- to light-brownish-gray-weathering, massive to bedded muscovite-biotite-chlorite metawacke, conglomerate, and blue-quartz pebbly phyllite, wacke and feldspathic quartzite. Cover rocks of the Lincoln Mountain massif and northwestern flank of the Green Mountain massif.

Bondville metadacite and trondhjemite gneiss (Middle Mesoproterozoic) at surface, covers 0.5 % of this area

Light-gray to whitish-gray, fine-grained biotite trondhjemitic gneiss, locally containing abundant magnetite. U-Pb zircon SHRIMP age of 1,342 Ma, no. 6B (Ratcliffe and others, 1991; Aleinikoff and others, 2011). South Londonderry Igneous Suite (Middle and Early Mesoproterozoic) (1,393±9 Ma to 1,309±6 Ma). Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Frontenac Formation (Devonian and Silurian) at surface, covers 0.5 % of this area

Thick-bedded, ankeritic, micaceous, and feldspathic metasandstones interlayered with subordinate dark-gray metapelite. Metasandstone beds commonly are rusty weathering and up to 4 m thick; calc-silicate lenses locally present. Part of the Connecticut Valley Trough.

Maidstone pluton (Devonian) at surface, covers 0.5 % of this area

Almost-white to dark-gray, locally pink, medium- to coarse-grained hypidiomorphic, granular, biotite-muscovite-microcline-plagioclase granite; accessories include apatite, sphene, pyrite, and magnetite. Igneous rocks of the Northeast Kingdom batholith of Ayuso and Arth (1992). Part of the New Hampshire Plutonic Suite.

Devonian intrusive rocks (Devonian) at surface, covers 0.5 % of this area

Binary and biotite granite and granodiorite, undifferentiated. Includes small dikes labeled Dg. Part of the New Hampshire Plutonic Suite.

Rawsonville trondhjemite gneiss (Early Mesoproterozoic) at surface, covers 0.4 % of this area

Chalky-white to light-gray-weathering, medium- to coarse-grained biotite metatrondhjemite and aplite (Y1rta). Dated sample with U-Pb zircon SHRIMP age of 1,367±16 Ma, no. 3 (Ratcliffe and others, 1991; Aleinikoff and others, 2011) from crest of Bromley Mountain; U-Pb zircon age of 1,348±3 Ma, no. 6 (Ratcliffe and others, 1991). South Londonderry Igneous Suite (Middle and Early Mesoproterozoic) (1,393±9 Ma to 1,309±6 Ma). Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Nulhegan pluton - inner zone (Devonian) at surface, covers 0.4 % of this area

Light-gray to dark-gray, medium- to coarse-grained, massive, biotite-clotted, hornblende-quartz monzodiorite, minor granodiorite, and granite. Rb/Sr whole-rock age of 390±14 Ma (Ayuso and Arth, 1992). Igneous rocks of the Northeast Kingdom batholith of Ayuso and Arth (1992). Part of the New Hampshire Plutonic Suite.

Middlebury Limestone (Middle Ordovician) at surface, covers 0.4 % of this area

Buff-streaked, dark-bluish-gray, thinly bedded and well-foliated dolomitic limestone, shown above the Champlain thrust south of Middlebury. Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

Stowe Formation - carbonaceous phyllite member (Cambrian and Neoproterozoic?) at surface, covers 0.4 % of this area

Interlayered grayish-green and rusty-weathering black quartzose phyllite, similar to dark carbonaceous phyllites of the Ottauquechee Formation (Co). Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks.

West Castleton Formation (Middle and Lower Cambrian) at surface, covers 0.4 % of this area

Dark-gray to black, fine-grained slate and phyllite, interbedded with thinly laminated bluish-black fine-grained limestone, limestone conglomerate. Unit is interbedded near the base with green phyllite and sooty-punky-weathering calcitic quartz wacke and limestone of the Browns Pond Formation, which is shown separately where mapped. Rocks of the Giddings Brook, Sunset Lake, and Bird Mountain slices. Part of the Taconic Allochthon.

Waits River Formation - Ayers Cliff member (Lower Devonian and Upper Silurian) at surface, covers 0.4 % of this area

Gray- to bluish-gray, fine- to medium-grained, thinly bedded calcareous metasandstone, quartzose metalimestone, and fissile, laminated calcareous metasandstone and phyllite. Part of the Connecticut Valley Trough.

Morses Line Slate (Ordovician) at surface, covers 0.4 % of this area

Medium-gray to black calcareous slate. Cover rocks of the Saint Albans area.

Gile Mountain Formation - Meetinghouse Slate member (Lower Devonian) at surface, covers 0.4 % of this area

Dark-gray slate and phyllite containing sparse to moderately abundant beds of light-gray, fine-grained metasandstone and metasiltstone, 1 mm to 1 cm thick. Part of the Connecticut Valley Trough.

Tibbit Hill Formation (Cambrian and Neoproterozoic) at surface, covers 0.4 % of this area

Largely metabasalt and minor metasedimentary rocks consisting of massive, fine-grained, dark-green metabasalt flows, pillow basalt, vesicular basalt composed of albite, epidote, chlorite (±actinolite); and interbedded phyllitic grits, feldspathic quartzite, chloritic metawacke, and basaltic tuffaceous metasedimentary rocks, all similar to rocks of the Pinnacle Formation. Volcanics are alkalic to transitional metabasalts. Cover rocks of the Lincoln Mountain massif and northwestern flank of the Green Mountain massif.

Cutting Dolostone (Lower Ordovician) at surface, covers 0.3 % of this area

Gray, thinly bedded dolomitic sandstone, grading upward into dolomitic limestone or mottled dolomitic marble. In southern Vermont east of the Taconic Range, unit is not recognized and may appear as sandy zones within rocks mapped as the Shelburne Marble. Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

Victory pluton (Devonian) at surface, covers 0.3 % of this area

A western zone of medium- to fine-grained biotite-muscovite granite and minor hornblende-biotite tonalite and an eastern, more melanocratic zone of biotite-hornblende quartz monzonite like that in the Nulhegan pluton, as well as biotite granodiorite. Igneous rocks of the Northeast Kingdom batholith of Ayuso and Arth (1992). Part of the New Hampshire Plutonic Suite.

Ironbound Mountain Formation (Lower Devonian) at surface, covers 0.3 % of this area

Medium-dark-gray to grayish-black lustrous slate, phyllite, and schist containing sparse to moderately abundant 1-mm to- 5-cm-thick beds of light-gray, fine-grained metasandstone and metasiltstone, commonly pyritiferous and calcareous. Some graded beds. Gradational contact with Dco above and Dir below. Interpreted to be correlative with the Meetinghouse Slate Member of the Gile Mountain Formation. Part of the Connecticut Valley Trough.

Willoughby pluton - main zone (Devonian) at surface, covers 0.3 % of this area

Light-gray to pink, medium- to very coarse grained, massive, miarolitic garnet-muscovite peraluminous leucogranite. Pegmatitic main zone. Rb/Sr whole-rock age of 376±9 Ma (Ayuso and Arth, 1992). Igneous rocks of the Northeast Kingdom batholith of Ayuso and Arth (1992). Part of the New Hampshire Plutonic Suite.

Danby Formation (Upper Cambrian) at surface, covers 0.3 % of this area

Thin, light-gray beds of vitreous quartzite and crossbedded sandy dolostone. Unit discontinuous in southern Vermont. Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

Walloomsac Formation (Upper Ordovician) at surface, covers 0.3 % of this area

Same description as Hortonville Formation - Dark-gray siliceous shale and phyllite containing thin beds of bluish-gray argillaceous limestone and minor beds of gray to tan quartzite. Grades into limy shales of the Stony Point Formation. Tectonically shredded, silty varieties near and on Whipstock Hill constitute the Whipstock Breccia Member of Potter (1972) (Oww). Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

Baileys Mills tonalitic gneiss (Early Mesoproterozoic) at surface, covers 0.3 % of this area

Light-gray to whitish-gray-weathering, medium-grained biotite-quartz-plagioclase gneiss flecked with coarse biotite. Contains numerous lenses of fine-grained amphibolite similar to amphibolites associated with calc-silicate rocks of the type Mount Holly Complex in Mount Holly, rather than coarser grained dioritic gneiss associated with the Cole Pond and Rawsonville gneisses. U-Pb zircon SHRIMP age of 1,383±13 Ma, no. 2 (Ratcliffe and others, 1991; Aleinikoff and others, 2011). South Londonderry Igneous Suite (Middle and Early Mesoproterozoic) (1,393±9 Ma to 1,309±6 Ma). Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Mount Abraham Formation (Cambrian and Neoproterozoic) at surface, covers 0.3 % of this area

Lustrous, silvery-green to bluish-gray, fine- to medium-grained, white mica-chloritoid-quartz-chlorite schist and phyllite, locally with minor garnet and magnetite porphyroblasts (CZap). Distinctive chlorite streaks and 1-cm rusty needles of altered kyanite are common. Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks.

Pinnacle Formation - metawacke and phyllite member (Cambrian and Neoproterozoic) at surface, covers 0.3 % of this area

Light-gray, medium-grained, massive quartz-sericite-chlorite-albite metawacke, gray to grayish-green magnetite-chlorite-muscovite-quartz schist, and phyllite or pebbly phyllite, locally rich in magnetite. Cover rocks of the Lincoln Mountain massif and northwestern flank of the Green Mountain massif.

Echo Pond pluton - granodiorite and granite (Devonian) at surface, covers 0.3 % of this area

Light-gray to pink, medium- to coarse-grained, massive, seriate to porphyritic granodiorite and granite. Igneous rocks of the Northeast Kingdom batholith of Ayuso and Arth (1992). Part of the New Hampshire Plutonic Suite.

Moretown Formation - chlorite schist member (Lower Ordovician to Cambrian?) at surface, covers 0.3 % of this area

Pale-greenish-gray, lustrous and nonlustrous chlorite-muscovite feldspathic schist and schistose granofels. Local richly garnetiferous variant (Omgt). Part of the metasedimentary host rocks of the North River Igneous Suite. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Stowe Formation - feldspathic quartzite (Cambrian and Neoproterozoic?) at surface, covers 0.3 % of this area

Interbedded feldspathic quartzite within unit CZsa. Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks.

Poultney Formation (Middle and Lower Ordovician) at surface, covers 0.3 % of this area

Dull-white and whitish-gray-weathering, and pale-green and gray, thinly bedded to laminated slate and phyllite. Has distinctive beds, 1 cm to several centimeters thick, of siliceous argillite and metasiltstone and locally abundant thin beds of micritic black limestone near the base, interbedded with dark slate. Contains graptolites ranging from Ibexian to Whiterockian (Berry, 1961). Rocks of the Giddings Brook, Sunset Lake, and Bird Mountain slices. Part of the Taconic Allochthon.

Carbonaceous phyllite and siltstone (Lower Cambrian and Neoproterozoic) at surface, covers 0.3 % of this area

Medium- to dark-gray carbonaceous phyllite, gray slate, and metasiltstone, locally containing light-gray, medium- to thick-bedded quartzite and dolomitic quartzite (CZbq). Unit resembles rocks of the Netop Formation but lacks the distinctive lenses and pods of bluish-gray dolostone of the Netop on Dorset Mountain, although lenses of whitish quartzite are present. Rocks of the Dorset Mountain slice (includes Dorset Mountain proper and Mount Equinox, southward to West Mountain near Bennington). Part of the Taconic Allochthon.

Waits River Formation - muscovite porphyroblastic carbonaceous schist member (staurolite-grade rocks) (Lower Devonian and Upper Silurian) at surface, covers 0.3 % of this area

Dark-gray to coaly-black, fine-grained plagioclase-muscovite-quartz schist and metawacke, shown southeast of Springfield; in part correlative with staurolite-grade rocks mapped as Littleton Formation (Dl) flanking the Vernon dome (shown as DSwb/Dl). Part of the Connecticut Valley Trough.

Compton Formation - metasandstone member (Lower Devonian) at surface, covers 0.3 % of this area

Light-gray to tan, micaceous, locally calcareous metasandstone and slate or metamudstone in beds a few centimeters to tens of centimeters thick. Graded bedding common. Interpreted to be correlative with the Gile Mountain Formation. Part of the Connecticut Valley Trough.

Bull Hill Gneiss of Richardson (1931) (Neoproterozoic) at surface, covers 0.3 % of this area

Light-pinkish-gray to gray, very coarse grained to medium-grained and mylonitic biotite-plagioclase-quartz-microcline augen gneiss; locally has large ovoidal relict microcline with rapakivi rims and intrusive breccia containing xenoliths of gneissic units of the Mount Holly Complex. Restricted to the Chester and Athens domes, occurring in the core as well as in fault slivers along the eastern and western margins, and tectonically intercalated with rocks of the Mount Holly Complex and the Hoosac Formation. U-Pb zircon upper-intercept ages of 945±7 Ma, no. 17, and 955±5 Ma, no. 18 (Karabinos and Aleinikoff, 1990). Cardinal Brook Intrusive Suite (965±4 Ma to 945±7 Ma). Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Dalton Formation - undivided (Lower Cambrian and Neoproterozoic) at surface, covers 0.3 % of this area

Heterogeneous unit consisting of rusty- to tan-weathering flaggy feldspathic quartzite, tan-weathering quartz phyllite, and feldspathic quartzite. Unit interfingers to the north with rocks of the Tyson Formation and to the east with rocks of the Hoosac Formation. Cover rocks of the Southern Green Mountains.

Chipman Formation - Beldens Member (Middle Ordovician) at surface, covers 0.3 % of this area

Light-gray to creamy-white-weathering fine-grained limestone, orangey-buff-weathering dolostone, and reddish-streaked (hematite) calcite marble. Chipman Formation (mapped south of Wings Point). Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

Washington Gneiss (Middle Mesoproterozoic) at surface, covers 0.3 % of this area

Dark-rusty-grayish-brown-weathering, graphitic garnet-plagioclase-biotite-quartz (±sillimanite) schist; rusty-weathering blue-quartz-ribbed quartz schist; and garnet quartzite and rusty-weathering layers of sulfidic calc-silicate rock. Exposed in southernmost part of Green Mountain massif. Distinctive quartz ribbing decreases northward where more aluminous, less quartzofeldspathic rocks are mapped as Y2rs. Part of the aluminous schists and gneisses of the Washington Gneiss and Wilcox Formation and related rocks. Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Ira Formation (Upper Ordovician) at surface, covers 0.3 % of this area

Same description as Hortonville Formation - Dark-gray siliceous shale and phyllite containing thin beds of bluish-gray argillaceous limestone and minor beds of gray to tan quartzite. Grades into limy shales of the Stony Point Formation. Unit mapped along east side of the Taconic allochthon south to Bennington. Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

Migmatitic gneiss (Middle Mesoproterozoic) at surface, covers 0.3 % of this area

Light-gray and pinkish-gray to yellowish-gray, massive, medium-grained plagioclase granitic gneiss, and migmatite-veined biotite-plagioclase gneiss. Occurs prominently in Jamaica, in Andover in the Chester dome, and in Weston where it appears to form an integral part of Y1,2bg, but also locally appears to be intrusive. A mixed rock of uncertain origin. U-Pb zircon SHRIMP age of 1,326±4 Ma, no. 8 (Aleinikoff and others, 2011), suggests affinity with metamorphic and igneous events associated with the Middle Mesoproterozoic Ludlow Mountain and Proctor Hill granodiorite gneisses of the South Londonderry Igneous Suite. Age of migmatization is younger than 1,326 Ma. Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Ammonoosuc Volcanics of Billings (1935) - metamorphosed andesitic and basaltic tuff, crystal tuff, and tuff breccia (Upper and Middle Ordovician) at surface, covers 0.3 % of this area

Dark-greenish-gray to medium-bluish-gray metamorphosed andesitic and basaltic tuff, crystal tuff, and tuff breccia; minor pillow lava. Commonly contains plagioclase and (or) altered mafic phenocrysts. Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt. Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt.

West Castleton and Hatch Hill(?) Formations - undifferentiated (Cambrian) at surface, covers 0.3 % of this area

Black slate and gray phyllite exposed on Woodlawn and Tinmouth Mountains in Pawlet and Tinmouth Townships, after usage of Shumaker and Thompson (1967). Rocks of the Giddings Brook, Sunset Lake, and Bird Mountain slices. Part of the Taconic Allochthon.

Cheshire Quartzite - argillaceous (Lower Cambrian) at surface, covers 0.3 % of this area

Locally contains a mappable brown-weathering, gray to brown argillaceous quartzite member. Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

Moretown Formation - carbonaceous and sulfidic schist member (Lower Ordovician to Cambrian?) at surface, covers 0.3 % of this area

Rusty-weathering, dark-gray biotite-muscovite-quartz (±garnet) schist, carbonaceous schist, and gray, splintery-fractured, biotitic sulfidic quartz schist. Contains layers of rusty-weathering amphibolite, coticule, and vitreous quartzite (Ombq). A prominent zone that extends from the north end of the Chester dome and near Proctorsville southward to near Townshend contains abundant ultramafic rocks (CZu). Part of the metasedimentary host rocks of the North River Igneous Suite. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Stowe Formation - kyanite schist member (Cambrian and Neoproterozoic?) at surface, covers 0.3 % of this area

Silvery-blue, medium- to coarse-grained chlorite-muscovite-quartz schist (±garnet±kyanite±chloritoid); contains characteristic spangly muscovite and elongated knots of quartz and layers of pinkish coticule, exposed in the Worcester Mountains. Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks.

Moretown Formation - granofels and phyllite member (Lower Ordovician to Cambrian?) at surface, covers 0.2 % of this area

Light-gray to tan, fine-grained albite-chlorite-sericite-quartz phyllitic quartzite interlayered with light-greenish-gray quartzofeldspathic granofels and dark-gray phyllite. Contains numerous boudinaged, massive to foliated, dark-green metamorphosed mafic dikes and sills. Part of the metasedimentary host rocks of the North River Igneous Suite. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Granitic gneiss of Lincoln Mountain massif (Middle Mesoproterozoic) at surface, covers 0.2 % of this area

Hetero-geneous unit consisting of medium-grained biotite-microcline-plagioclase gneiss and pinkish-gray, medium- to coarse-grained microcline-perthite granitic gneiss. Interpreted as intrusive granitic rock older than Y3 rocks of Chittenden Intrusive Suite. Stratton Mountain Intrusive Suite (Middle Mesoproterozoic) (1,244±8 Ma to 1,221±4 Ma). Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Chipman Formation - Bridport Member (Middle Ordovician) at surface, covers 0.2 % of this area

Thickly bedded, “beeswax-scored,” orangey-beige-weathering, yellowish-gray to light-bluish-gray dolostone, dark-gray fine-grained to aphanitic dolostone, and minor beds of bluish-gray limestone. Transitions eastward into the Beldens Member with addition of limestone beds. Equivalent to Providence Island Dolostone (Ofcpi). Chipman Formation (mapped south of Wings Point). Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

Harriman Reservoir Granite (Neoproterozoic) at surface, covers 0.2 % of this area

Light-gray to pinkish-gray, biotite-plagioclase-microcline megacrystic granite and augen gneiss; rapakivi texture locally preserved. Unit occurs in the Rayponda and Sadawga domes. Cardinal Brook Intrusive Suite (965±4 Ma to 945±7 Ma). Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Partridge Formation (Upper Ordovician) at surface, covers 0.2 % of this area

Dark-gray to grayish-black, rusty-weathering sulfidic slate and phyllite interlayered with felsic volcanic rocks and tuffs, and amphibolite (Opa). Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt.

Rowe Schist - amphibolite and greenstone member (Cambrian and Neoproterozoic?) at surface, covers 0.2 % of this area

Predominantly very dark green to black, finely foliated biotite-plagioclase amphibolite to dark-green to light- greenish-gray, chlorite-plagioclase-ankerite greenstone and interlayered gray biotitic feldspathic volcaniclastic rock and feldspathic quartzite. Amphibolites have transitional basalt to MORB compositions; greenstones have MORB compositions. Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks. Rowe Schist: Mapped in southern Vermont where the uppermost part is continuous with amphibolites, schists, and feldspathic schists of the Rowe Schist of Massachusetts. These upper units are continuous with rocks of the Stowe Formation to the north. Units in the middle and lowermost structural positions (above the Hoosac Formation) are in a similar structural position as rocks of the Ottauquechee and Pinney Hollow Formations, although structural continuity and correlations with the Ottauquechee and Pinney Hollow Formations are uncertain owing to extensive structural duplication by thrust faulting and folding.

Waits River Formation - mafic member (Lower Devonian and Upper Silurian) at surface, covers 0.2 % of this area

Massive, coarse-grained hornblende-plagioclase gneiss and granofels; finely foliated hornblende-plagioclase amphibolite; actinolite-epidote-chlorite greenstone. Part of the Connecticut Valley Trough.

Moretown Formation - hornblende fascicule schist and granofels member (Lower Ordovician to Cambrian?) at surface, covers 0.2 % of this area

Light-gray to grayish-green chlorite-muscovite-biotite-plagioclase-quartz schist, conspicuous sprays of hornblende, and biotite-hornblende-plagioclase granofels. Part of the metasedimentary host rocks of the North River Igneous Suite. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Nulhegan pluton - core (Devonian) at surface, covers 0.2 % of this area

Quartz monzonite. Rb/Sr whole-rock age of 390±14 Ma (Ayuso and Arth, 1992). Igneous rocks of the Northeast Kingdom batholith of Ayuso and Arth (1992). Part of the New Hampshire Plutonic Suite.

Bull Formation - Bomoseen Graywacke member (Neoproterozoic) at surface, covers 0.2 % of this area

Pale-reddish-brown to light-gray-weathering, medium- and fine-grained, massive to thickly bedded, olive-green to gray micaceous quartz-feldspar graywacke and siltstone, locally containing coarse detrital muscovite, biotite, and autoclastic slate chips. Resembles finer grained parts of the Rensselaer Graywacke Member of the Nassau Formation (of Potter, 1972), and the Bird Mountain Grit (of Dale, 1900). Unit interfingers with and grades laterally into the Mettawee slate facies. In the Mt. Anthony area is shown as CZnb (Bomoseen Member of the Nassau Formation of Potter, 1972). Rocks of the Giddings Brook, Sunset Lake, and Bird Mountain slices. Part of the Taconic Allochthon.

Tyson Formation - quartz-pebble phyllite and wacke member (Lower Cambrian and Neoproterozoic) at surface, covers 0.2 % of this area

Gray to grayish-green, biotite-chlorite-quartz-pebble phyllite; albitic metawacke is similar to metawacke member of the Pinnacle Formation but more thinly bedded and contains less metawacke. Albitic biotite-(chlorite)-quartz granofels and wacke locally present. Eastern and western flank of the Green Mountain massif.

West Bridgewater Formation (Middle Ordovician) at surface, covers 0.2 % of this area

Black to dark-gray, sulfidic to nonsulfidic, carbonaceous, fine-grained, well-foliated biotite-muscovite-quartz phyllite; contains pods and thin beds of medium-dark-gray and gray-and-white-mottled dolostone, thin beds of ankeritic quartzite, and, in upper part, rhythmically layered gray quartzite, limestone breccia and laminated silicic phyllite. Dolostone contains Middle Ordovician conodonts (Ibexian to mid-Whiterockian at West Bridgewater and Whiterockian at Buels Gore and West Bolton (Ratcliffe and others, 1999; Thompson and others, 2002). Cover rocks north of the Lincoln Mountain massif.

Parker Slate (Cambrian) at surface, covers 0.2 % of this area

Black arenaceous slate with dolomite horizons; interbedded dolostone and sandstone breccia in a dolostone matrix; and massive dolostone with thin sandstone beds. Cover rocks of the Saint Albans area.

Rowe Schist - chlorite phyllite member (Cambrian and Neoproterozoic?) at surface, covers 0.2 % of this area

Pale-green to dark-green, lustrous, magnetite-chlorite-muscovite-quartz phyllite and schist, highly tectonically laminated near larger ultramafic bodies (CZu). Unit typical of lustrous chloritic schists of the Stowe Formation farther north. Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks. Rowe Schist: Mapped in southern Vermont where the uppermost part is continuous with amphibolites, schists, and feldspathic schists of the Rowe Schist of Massachusetts. These upper units are continuous with rocks of the Stowe Formation to the north. Units in the middle and lowermost structural positions (above the Hoosac Formation) are in a similar structural position as rocks of the Ottauquechee and Pinney Hollow Formations, although structural continuity and correlations with the Ottauquechee and Pinney Hollow Formations are uncertain owing to extensive structural duplication by thrust faulting and folding.

Moretown Formation - Whetstone Hill Member - phyllite facies (Lower Ordovician to Cambrian?) at surface, covers 0.2 % of this area

Predominantly medium-dark-gray to lustrous-tan, fine-grained garnet-biotite-muscovite phyllite and carbonaceous phyllite; contains layers of dark-gray quartzite, coticule, and ironstone, locally mapped separately. Part of the metasedimentary host rocks of the North River Igneous Suite. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Stowe Formation - metadiabase dikes (Cambrian and Neoproterozoic?) at surface, covers 0.2 % of this area

Part of unit CZs local areas rich in metadiabase dikes. Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks.

Cram Hill Formation - undivided (Middle? and Early Ordovician) at surface, covers 0.2 % of this area

Predominantly dark-gray to grayish-green quartz-chlorite-(biotite)-muscovite phyllite; contains 1- to 2-cm-thick beds of dark-gray metasiltstone and quartzite, and thicker beds of dark-bluish-gray vitreous quartzite, grayish-green to light-yellowish-green sericite phyllite (felsic tuffs) and cobble to boulder conglomerate, and greenstone. Mapped north of the Braintree Intrusive Complex and near Brattleboro. Part of the metasedimentary host rocks of the North River Igneous Suite. Cram Hill Formation: western part of the Cram Hill Formation is in part correlative with Whetstone Hill Member of the Moretown Formation. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Hoosac Formation - biotite phyllite member (Lower Cambrian and Neoproterozoic) at surface, covers 0.2 % of this area

Coal-black, lustrous, rusty- to non-rusty-weathering, biotite-muscovite-plagioclase-quartz schist and phyllite, containing lenses of white laminated quartzite as beds and discoidal boudins. Eastern flank of the Green Mountain massif and eastern domes.

Pawlet Formation (Upper Ordovician) at surface, covers 0.2 % of this area

Light-gray, tan-weathering, mica-speckled, massive to thin-bedded quartz-plagioclase wacke interbedded with dark-gray carbonaceous slate. Contains distinctive autoclastic chips of gray slate, fragments of dacitic to andesitic volcanics, and subangular clasts of dark-gray quartz and oligoclase. Interbedded black slates contain graptolites of the C. bicornis Biozone (see Webby and others, 2004, fig. 2.1) (lower to middle Mohawkian). Interpreted as uncomformable on rocks as old as the Hatch Hill Formation and possibly the West Castleton Formation of the allochthon. Unit is indistinguishable from beds in the Austin Glen Graywacke (after Potter, 1972) (Oag) interpreted as synorogenic autochthonous rocks. Rocks of the Giddings Brook, Sunset Lake, and Bird Mountain slices. Part of the Taconic Allochthon.

Stamford Granite - rapakivi granite (Neoproterozoic) at surface, covers 0.2 % of this area

Light-gray to medium-gray, very coarse grained biotite-plagioclase-microcline rapakivi granite; contains large megacrysts of microcline perthite having rims of plagioclase that contain inclusions of biotite and garnet. Unit includes lesser irregular dikes and segregations of hornblende-biotite ferrodiorite and ferromonzonite. U-Pb zircon upper-intercept age of 962±1 Ma, no. 20 (revised from Karabinos and Aleinikoff, 1990). Cardinal Brook Intrusive Suite (965±4 Ma to 945±7 Ma). Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Moretown Formation - amphibolite and greenstone member (Lower Ordovician to Cambrian?) at surface, covers 0.2 % of this area

Includes light-pale-green chloritic ankeritic greenstone; black, and fine-grained hornblende-plagioclase (±garnet±epidote) amphibolite. Part of the metasedimentary host rocks of the North River Igneous Suite. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Derby pluton - granodiorite and tonalite (Devonian) at surface, covers 0.2 % of this area

Light-gray, medium- to coarse-grained, massive, epidote-biotite-muscovite porphyritic granodiorite and minor tonalite. Rb/Sr whole-rock isochron age of 370±17 Ma (Ayuso and Arth, 1992). Igneous rocks of the Northeast Kingdom batholith of Ayuso and Arth (1992). Part of the New Hampshire Plutonic Suite.

Albee Formation - Scarritt member (Ordovician and Cambrian) at surface, covers 0.2 % of this area

Dark-gray slate interlayered with thin beds of light-gray, fine-grained micaceous and feldspathic metasandstone (typically ribby weathering). Abruptly graded beds <1 cm to 30 cm thick are locally common as is channeling and, in places, soft-sediment deformation. Commonly sulfidic and rusty weathering. Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt.

Nassau Formation of Potter (1972) - Mettawee member (Neoproterozoic) at surface, covers 0.2 % of this area

Predominantly greenish-gray to pale-lustrous-green chlorite-muscovite-quartz phyllite; and green and purple, bedded and mottled phyllite. Locally contains boudins and thin beds of limestone and pods of pinkish-gray to cream-white dolostone, and minor quartzite. Unit interfingers with the West Castleton Formation above and laterally grades into the Bomoseen Graywacke Member. Also shown as CZnm (Mettawee Member of the Nassau Formation of Potter, 1972). Rocks of the Giddings Brook, Sunset Lake, and Bird Mountain slices. Part of the Taconic Allochthon.

Pinney Hollow Formation - amphibolite and greenstone member (Cambrian and Neoproterozoic) at surface, covers 0.2 % of this area

Dark-green to black plagioclase-biotite-hornblende (±quartz) amphibolite, epidote amphibolite, and ankeritic-chlorite-magnetite-plagioclase (albite) greenstone. Shows all gradations from massive but well-foliated metabasalt to well-bedded basaltic volcaniclastic rock and volcanic metawacke. Cover rocks of Green Mountain anticlinorium.

Biddie Knob Formation (Lower Cambrian and Neoproterozoic) at surface, covers 0.2 % of this area

Predominantly green, purple and purplish-red, chloritic hematitic slate and phyllite, massive to thinly bedded. Has rare thin beds of white vitreous quartzite and contains abundant chloritoid. Underlies the Bird Mountain Grit (of Dale, 1900) and grades into the green slate of the Mettawee slate facies in the Bull Formation, probably in part correlative with the green phyllite member of the Netop Formation (CZngs) of the Dorset Mountain slice. Rocks of the Giddings Brook, Sunset Lake, and Bird Mountain slices. Part of the Taconic Allochthon.

Newark pluton (Devonian) at surface, covers 0.2 % of this area

Pinkish-gray to cream-colored, medium- to coarse-grained magnetite-microcline-perthite-biotite granite. Igneous rocks of the Northeast Kingdom batholith of Ayuso and Arth (1992). Part of the New Hampshire Plutonic Suite.

Proctor Hill granodiorite gneiss (Middle Mesoproterozoic) at surface, covers 0.2 % of this area

Gray to pinkish-gray, gneissoid magnetite-biotite-microcline-perthite granodiorite, and locally microcline megacrystic gneissic granite, well-foliated and highly variable in composition, having aplitic and hornblende-rich reaction zones (Y2pha) where in contact with calc-silicate rocks. Crosscuts all paragneiss units; is a thoroughly gneissic rock. Correlated with the Ludlow Mountain granodiorite gneiss. South Londonderry Igneous Suite (Middle and Early Mesoproterozoic) (1,393±9 Ma to 1,309±6 Ma). Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Hoosac Formation - albite schist and granofels member (Lower Cambrian and Neoproterozoic) at surface, covers 0.2 % of this area

Rusty-weathering, medium- to dark-gray, black albite-biotite-quartz schist and granofels, marked by large spangles of muscovite and weathered-out pits of dolomite or ankerite. Eastern flank of the Green Mountain massif and eastern domes.

Stowe Formation - amphibolite member (Cambrian and Neoproterozoic?) at surface, covers 0.2 % of this area

Dark-green to black, massive, medium- to coarse-grained, layered albite-epidote-hornblende amphibolite; possibly is a meta-intrusive. Exposed in the Worcester Mountains. Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks.

Lost Nation granite (Early Silurian to Middle Ordovician) at surface, covers 0.2 % of this area

Foliated biotite and (or) hornblende granite; locally diorite and lesser amounts of gabbro. Where present, potassium feldspar is microcline. Contact aureole is in the Albee Formation. U-Pb zircon ages of 442±4 Ma, no. 30 (Moench and Aleinikoff, 2003), and 444.1±2.1 Ma, no. 29 (Rankin and Tucker, 2009); and U-Pb sphene age of 443±3 Ma, no. 31 (Moench and Aleinikoff, 2003). Part of the Highlandcroft Plutonic Suite: Epizonal to mesozonal, foliated and metamorphosed (greenschist facies) plutons exposed northwest of the Ammonoosuc fault. Compositions range from granite to diorite to lesser amounts of gabbro. Part of the Bronson Hill arch intrusive rocks.

Hornblende-plagioclase gneiss (Middle Mesoproterozoic) at surface, covers 0.1 % of this area

Medium- to coarse-grained hornblende dioritic-appearing gneiss. Part of the aluminous schists and gneisses of the Washington Gneiss and Wilcox Formation and related rocks. Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Moretown Formation - garnet schist member (Lower Ordovician to Cambrian?) at surface, covers 0.1 % of this area

Greenish-gray feldspathic garnet schist; grades into Omfs. Part of the metasedimentary host rocks of the North River Igneous Suite. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Forestdale Formation - dolostone member (Lower Cambrian and Neoproterozoic) at surface, covers 0.1 % of this area

Upper part of CZfd consists of orangey-tan- to brown-weathering quartz-pebble dolostone and dolomitic crossbedded feldspathic metasandstone; lower part of CZfd largely cream- to beige-weathering massive dolostone. Cover rocks of the Lincoln Mountain massif and northwestern flank of the Green Mountain massif.

Felchville Gneiss - aplitic facies (Early Mesoproterozoic) at surface, covers 0.1 % of this area

Light-gray to whitish-gray, fine-grained, magnetite trondhjemitic gneiss and aplitic trondhjemite, intricately intrusive into layered paragneisses of the Chester dome; contains xenoliths of more mafic gneiss. U-Pb zircon SHRIMP age of 1,372±11 Ma, no. 4 (Aleinikoff and others, 2011). Similar fine-grained magnetite aplitic gneisses exposed in the Green Mountain massif are associated with tonalitic gneisses on Torment Hill, Weston. South Londonderry Igneous Suite (Middle and Early Mesoproterozoic) (1,393±9 Ma to 1,309±6 Ma). Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Hoosac Formation - garnet schist member (Lower Cambrian and Neoproterozoic) at surface, covers 0.1 % of this area

Lustrous, green, ilmenite-chlorite-chloritoid-garnet-muscovite-quartz (±paragonite) schist; resembles Pinney Hollow Formation but lacks amphibolite. Aluminous schists at Devils Den and aluminous rocks of the Cavendish Formation may be correlative. Eastern flank of the Green Mountain massif and eastern domes.

Crown Point Formation (Middle Ordovician) at surface, covers 0.1 % of this area

Gray, massively bedded fossiliferous limestone. Part of the Chazy Group. Rocks of the Laurentian Margin. Part of the Adirondack lowlands and Lake Champlain lowlands (west of the Orwell and Champlain thrusts). Also part of the Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

Barnard Gneiss proper (of Richardson, 1924) (Ordovician and Late Cambrian) at surface, covers 0.1 % of this area

Predominantly light-gray to whitish-weathering, massive to gneissic hornblende-biotite tonalite and biotite-muscovite-quartz-plagioclase trondhjemite; includes rare hornblendite, metadiabase, and metapyroxenite as small stocks, inclusions, and dikes. U-Pb zircon SHRIMP age of 496±8 Ma north of Proctorsville, no. 23 (Aleinikoff and others, 2011); U-Pb zircon age of 471.4±3.7 Ma south of Bethel, no. 26 (Karabinos and others, 1998). North River Igneous Suite (502±4 Ma to 471.4±3.7 Ma): collection of metatonalite, metatrondhjemite, and metabasalt occurring as intrusive dikes, sills, and small stocks, and possibly meta-andesite and metadacitic tuffs. Correlative with extrusive dacitic metavolcanic and meta-andesitic rocks of the Moretown and Cram Hill Formations. Coextensive in part with igneous rocks of the Hawley Formation of Massachusetts. Part of the Volcanic-arc intrusive and volcanic rocks of the North River Igneous Suite of the Rowe-Hawley zone. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Cram Hill Formation - gray quartz schist member (Middle? and Early Ordovician) at surface, covers 0.1 % of this area

Rusty-grayish-brown-weathering, locally splintery-fractured, dark-gray to steel-gray biotite-quartz-feldspathic schist and quartzite and interbedded carbonaceous, small-garnet papery muscovite phyllite and schist similar to Ochs. Part of the metasedimentary host rocks of the North River Igneous Suite. Cram Hill Formation: western part of the Cram Hill Formation is in part correlative with Whetstone Hill Member of the Moretown Formation. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Quartzite - undifferentiated (Middle Mesoproterozoic) at surface, covers 0.1 % of this area

Tan to rusty-brown or gray, thinly layered garnet-biotite quartzite and schistose quartzite associated with aluminous schists and calc-silicate rocks or interbedded within biotite-quartz-plagioclase paragneiss. Unit probably occurs at various stratigraphic levels; may be Early Mesoproterozoic in part (Y1q). Part of the aluminous schists and gneisses of the Washington Gneiss and Wilcox Formation and related rocks. Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Nulhegan pluton - western zone (Devonian) at surface, covers 0.1 % of this area

Light-gray to dark-gray, medium- to coarse-grained, massive, biotite-clotted, hornblende-quartz monzodiorite, minor granodiorite, and granite. Rb/Sr whole-rock age of 390±14 Ma (Ayuso and Arth, 1992). Igneous rocks of the Northeast Kingdom batholith of Ayuso and Arth (1992). Part of the New Hampshire Plutonic Suite.

Orwell Limestone (Upper Ordovician) at surface, covers 0.1 % of this area

Dove-gray-weathering, black to dark- gray, fine-grained poorly fossiliferous limestone. Distinguished from the Middlebury Limestone with difficulty, especially in the area west of the Sudbury slice. Part of the Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts). Rocks of the Laurentian Margin. Also part of the Adirondack lowlands and Lake Champlain lowlands (west of the Orwell and Champlain thrusts).

Chipman Formation - Weybridge Member (Middle Ordovician) at surface, covers 0.1 % of this area

Light-gray to cream-colored fine-grained calcite marble, and thin dolomitic layers, locally crossbedded; may occur as lenses at several positions within the Beldens Member. Chipman Formation (mapped south of Wings Point). Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

Hoosac Formation - Turkey Mountain metabasalt member (Lower Cambrian and Neoproterozoic) at surface, covers 0.1 % of this area

Dark-green to black, hornblende-plagioclase (±garnet±epidote) amphibolite and grayish-green epidote-plagioclase ankeritic greenstone; grades into epidote-quartz-plagioclase volcaniclastic wacke. Occurs as lenses at multiple stratigraphic levels. Lower layers are transitional and alkalic metabasalts; higher units are typical midocean ridge basalt (MORB)-type metabasalts. Eastern flank of the Green Mountain massif and eastern domes.

Amphibolite (Middle Mesoproterozoic) at surface, covers 0.1 % of this area

Dark-grayish-green, fine-grained quartz-hornblende-plagioclase amphibolite, locally garnetiferous, and medium-grained hornblende-plagioclase amphibolite. Occurs with belts of calc-silicate rocks and as lenses within biotite-quartz-plagioclase paragneiss. Unit probably includes both meta-igneous and metasedimentary rocks intercalated throughout the Early and Middle Mesoproterozoic-age rocks of the Mount Holly Complex. Part of the aluminous schists and gneisses of the Washington Gneiss and Wilcox Formation and related rocks. Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Moretown Formation - interbedded quartzite and phyllite member (Lower Ordovician to Cambrian?) at surface, covers 0.1 % of this area

Light-gray laminated quartzite and vitreous quartzite interbedded with gray phyllite and schist. Part of the metasedimentary host rocks of the North River Igneous Suite. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Branch Brook dike and sill complex - South Pond facies (Ordovician and Late Cambrian) at surface, covers 0.1 % of this area

Light- to dark-gray and steel-blue to apple-green, fine- grained hornblende-chlorite-plagioclase amphibolite, locally containing significant calcite and pyrite and interlayered felsic layers of metatrondhjemite or metadacite. Similar in part to the mixed gneiss facies (Onbm). North River Igneous Suite (502±4 Ma to 471.4±3.7 Ma): collection of metatonalite, metatrondhjemite, and metabasalt occurring as intrusive dikes, sills, and small stocks, and possibly meta-andesite and metadacitic tuffs. Correlative with extrusive dacitic metavolcanic and meta-andesitic rocks of the Moretown and Cram Hill Formations. Coextensive in part with igneous rocks of the Hawley Formation of Massachusetts. Part of the Volcanic-arc intrusive and volcanic rocks of the North River Igneous Suite of the Rowe-Hawley zone. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Meta-ultramafic rocks - undifferentiated (Cambrian and Neoproterozoic) at surface, covers 0.1 % of this area

Brown to white-weathering, green, massive, moderately to fully serpentinized dunite and peridotite and schistose serpentinite; rusty-weathering, medium-grained talc-carbonate rock and quartz-carbonate (magnesite) rock. Part of Ultramafic rocks: occur as tectonic slivers and olistoliths in blocks within the Hazens Notch, Ottauquechee, Stowe, Rowe, and Moretown Formations. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Waits River Formation - volcaniclastic rock member (Lower Devonian and Upper Silurian) at surface, covers 0.1 % of this area

Silvery-grayish-green to light-gray, muscovite-biotite (chlorite)-plagioclase-quartz schist and granofels. Part of the Connecticut Valley Trough.

Whitehall Formation - dolostone (Lower Ordovician and Upper Cambrian) at surface, covers 0.1 % of this area

Predominantly light-gray and pinkish-gray, coarse-grained dolostone and cherty dolostone. Part of the Beekmantown Group. Rocks of the Laurentian Margin. Part of the Adirondack lowlands and Lake Champlain lowlands (west of the Orwell and Champlain thrusts).

Monastery Formation (Cambrian and Neoproterozoic) at surface, covers 0.1 % of this area

Heterogeneous unit consisting of coarse-grained, gray- to rusty-brown-weathering garnet-biotite-muscovite-quartz schist, gray albitic biotite-quartz granofels, well-bedded light-gray to steel-gray biotite, minor epidote-magnetite-actinolite-chlorite feldspathic wacke, and, near base, grayish-green laminated chlorite-muscovite-albite granofels and phyllite. Unit mapped in Hancock and Ripton in part as lateral equivalent of the Tyson Formation to the south and the Underhill Formation to the north. Eastern flank of the Green Mountain massif and eastern domes.

Tillotson Peak Structural Complex - albite gneiss (Cambrian) at surface, covers < 0.1 % of this area

White, light-gray- and green-banded, medium-grained, well-layered epidote-white mica-quartz-albite (±garnet±magnetite) gneiss with plagioclase and polycrystalline quartz porphyroblasts. Green, chloritic layers 2 to 10 cm thick also contain chlorite pseudomorphs after garnet. Gneiss is similar to gneiss at the base of the Belvidere Mountain Structural Complex. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Beekmantown Group, undivided (Middle Ordovician to Upper Cambrian) at surface, covers < 0.1 % of this area

Gray limestones, fossiliferous limestones, and dolostones. Rocks of the Laurentian Margin. Part of the Adirondack lowlands and Lake Champlain lowlands (west of the Orwell and Champlain thrusts).

Ammonoosuc Volcanics of Billings (1935) - undivided (Upper and Middle Ordovician) at surface, covers < 0.1 % of this area

A heterogeneous unit of interlayered and interfingering metamorphosed volcanic, volcaniclastic, and sedimentary rocks. Compositions range from basalt to sodic rhyolite. Fragmental rocks dominate (tuff to tuff breccia), but include sparse mafic pillow lava and felsic lava. Sedimentary protoliths include dark-gray sulfidic shale, ironstone, siltstone, graywacke, volcanic conglomerate, and rare limestone. Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt.

Dalton Formation - dark phyllite member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Dark-gray to gray, rusty-weathering, well-laminated tourmaline-biotite-muscovite-quartz phyllite containing thin beds of laminated quartzite. Resembles dark phyllite of the Moosalamoo Formation (CZmp), with which it is in part correlative. Unit interfingers to the north with rocks of the Tyson Formation and to the east with rocks of the Hoosac Formation. Cover rocks of the Southern Green Mountains.

Hornblende diorite gneiss (Early Mesoproterozoic) at surface, covers < 0.1 % of this area

Coarse-grained hornblende-plagioclase (±quartz) dioritic gneiss and gabbroic gneiss mapped in the Londonderry area, where it is interpreted as metagabbro and has a U-Pb zircon SHRIMP age of 1,393±9 Ma, no. 1 (Aleinikoff and others, 2011). South Londonderry Igneous Suite (Middle and Early Mesoproterozoic) (1,393±9 Ma to 1,309±6 Ma). Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Somerset Reservoir Granite - rapakivi granite and pegmatitic granite (Neoproterozoic) at surface, covers < 0.1 % of this area

Light-pinkish-gray-weathering, biotite-microcline-perthite or porphyritic rapakivi granite and pegmatitic granite; where deformed is a mylonitic augen gneiss. U-Pb zircon upper-intercept age of 965±4 Ma, no. 19 (Karabinos and Aleinikoff, 1990). Cardinal Brook Intrusive Suite (965±4 Ma to 945±7 Ma). Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Newport Intrusive Complex - granodiorite (Late Silurian) at surface, covers < 0.1 % of this area

Tan to light-bluish-gray, brown-weathering, medium- to coarse-grained, equigranular to porphyritic foliated granodiorite composed of quartz, plagioclase, perthite, microcline, biotite, and sericite. Part of the Lake Memphremagog Intrusive Suite (425±3 Ma to 418.5±2 Ma).

Felchville Gneiss - trondhjemite facies (Early Mesoproterozoic) at surface, covers < 0.1 % of this area

Light-gray to whitish-gray-weathering, magnetite-biotite-microcline-quartz-plagioclase metatrondhjemite to granodioritic gneiss; intrudes paragneiss units of the Chester dome. U-Pb zircon SHRIMP age of 1,370±11 Ma, no. 5 (Aleinikoff and others, 2011). South Londonderry Igneous Suite (Middle and Early Mesoproterozoic) (1,393±9 Ma to 1,309±6 Ma). Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Echo Pond pluton - gabbro and diorite (Devonian) at surface, covers < 0.1 % of this area

Outer zone of quartz gabbro and quartz diorite. Igneous rocks of the Northeast Kingdom batholith of Ayuso and Arth (1992). Part of the New Hampshire Plutonic Suite.

Fayston Formation - schist member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Silvery-green to rusty-tan, fine-grained chlorite-quartz-sericite (±garnet±chloritoid±allanite) schist and phyllite. Resembles green phyllites of the Pinney Hollow Formation (CZph) and Mount Abraham Forma-tion (CZa) and chloritic phyllite (CZtg) of the Tyson Formation. Cover rocks north of the Lincoln Mountain massif.

Hoosac Formation - undivided (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Heterogeneous unit consisting mainly of dark-gray to medium-light-gray-weathering, white-plagioclase-studded schist, gray slabby quartz-rich muscovite (±garnet) schist, and layers of dark-gray biotitic quartzite and metawacke. Eastern flank of the Green Mountain massif and eastern domes.

Newfane tonalite (Ordovician and Late Cambrian) at surface, covers < 0.1 % of this area

Light-gray to cream-weathering, massive to gneissic, hornblende-biotite and muscovite-biotite metatrondhjemite and metatonalite. Forms a thick, sill-like intrusive extending northward from South Newfane, where it intrudes metavolcanics (Ochv) of the Cram Hill Formation. U-Pb zircon SHRIMP age of 502±4 Ma, no. 22 (Aleinikoff and others, 2011). North River Igneous Suite (502±4 Ma to 471.4±3.7 Ma): collection of metatonalite, metatrondhjemite, and metabasalt occurring as intrusive dikes, sills, and small stocks, and possibly meta-andesite and metadacitic tuffs. Correlative with extrusive dacitic metavolcanic and meta-andesitic rocks of the Moretown and Cram Hill Formations. Coextensive in part with igneous rocks of the Hawley Formation of Massachusetts. Part of the Volcanic-arc intrusive and volcanic rocks of the North River Igneous Suite of the Rowe-Hawley zone. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Branch Brook dike and sill complex - Whitneyville facies (Ordovician and Late Cambrian) at surface, covers < 0.1 % of this area

Light-green to medium-green, massive, epidote-ilmenite-sphene-chlorite-hornblende-plagioclase amphibolite, marked by coarse hornblende and abundant phenocrysts of plagioclase. North River Igneous Suite (502±4 Ma to 471.4±3.7 Ma): collection of metatonalite, metatrondhjemite, and metabasalt occurring as intrusive dikes, sills, and small stocks, and possibly meta-andesite and metadacitic tuffs. Correlative with extrusive dacitic metavolcanic and meta-andesitic rocks of the Moretown and Cram Hill Formations. Coextensive in part with igneous rocks of the Hawley Formation of Massachusetts. Part of the Volcanic-arc intrusive and volcanic rocks of the North River Igneous Suite of the Rowe-Hawley zone. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Ottauquechee Formation - metawacke member (Cambrian) at surface, covers < 0.1 % of this area

Tan to gray phyllitic metawacke composed of rounded to angular grains of quartz, blue quartz, albite, and traces of detrital rock fragments in a fine-grained matrix of quartz, sericite, and chlorite. Feldspathic metawacke is common; quartz grains range in size from 0.5 mm to 0.5 cm. Conglomerate and breccia occur locally at The Knob (northwest of Lake Eden) and just north of the Lowell-Westfield town line. Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks.

Granulose albitic gneiss (Mesoproterozoic?) at surface, covers < 0.1 % of this area

Massive to poorly layered, highly lineated, light-tannish-gray to grayish-green, medium-grained, granulose, epidote-magnetite-biotite (chlorite)-muscovite-albite-quartz gneiss, veined with magnetite; spots of ankerite and clots of chlorite after original amphibole, pyroxene, or garnet are common. Highly altered rock is perhaps metasomatic and related to 1,170- to 1,120-Ma period of granitic intrusions. Unit shows all gradations from pinkish-gray biotite-quartz-plagioclase gneiss having centimeter-thick veins of garnet-bearing albitic micropegmatite, to nonlayered albitic granulose white gneiss. Occurs in central Green Mountain massif from Plymouth to Shrewsbury, on Robinson Hill, and along the eastern margin of the Green Mountain massif east of Rutland. Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Microcline-augen granite and monzogranite gneiss (Late Mesoproterozoic) at surface, covers < 0.1 % of this area

Gray to whitish-gray, coarse-grained biotite-microcline megacrystic granite and monzogranitic gneiss; passes locally into more equigranular granitic gneiss (Y3Ag) and locally into extensive areas of biotite pegmatoid granitic gneiss (Y3Apg), locally muscovite-bearing. Enclaves of metasedimentary units in these granites and associated gneisses are locally albitized and enriched in magnetite; enclaves of highly aluminous altered rocks now contain restites of chloritoid and abundant sericite. U-Pb zircon ages of 1,119±3.3 Ma (no. 15) and 1,121±1.4 Ma (no. 14) determined on samples near Sherburne Center and on Telegraph Hill east of Chittenden Reservoir by Karabinos and Aleinikoff (1990). Chittenden Intrusive Suite (1,149±8 Ma to 1,119±3 Ma). Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Mixed felsic and mafic rocks (Ordovician and Late Cambrian) at surface, covers < 0.1 % of this area

Heterogeneous composite intrusive well-layered unit consisting of biotite and hornblende metatrondhjemite, garnet-hornblende-plagioclase amphibolite, and metadiabase dikes; locally called Ruger Hill facies (Onr) in the Spring Hill syncline (Ratcliffe and Armstrong, 2001). Layering thickness ranges from 5 cm to 1 m. Unit may be in part metavolcanic as well as intrusive. Resembles well-layered undated felsic and mafic volcanics intercalated with metasediments of the Cram Hill Formation (Ochv). North River Igneous Suite (502±4 Ma to 471.4±3.7 Ma): collection of metatonalite, metatrondhjemite, and metabasalt occurring as intrusive dikes, sills, and small stocks, and possibly meta-andesite and metadacitic tuffs. Correlative with extrusive dacitic metavolcanic and meta-andesitic rocks of the Moretown and Cram Hill Formations. Coextensive in part with igneous rocks of the Hawley Formation of Massachusetts. Part of the Volcanic-arc intrusive and volcanic rocks of the North River Igneous Suite of the Rowe-Hawley zone. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Wilcox Formation (Middle Mesoproterozoic) at surface, covers < 0.1 % of this area

Lustrous to rusty-weathering biotite-muscovite (±chloritoid) schist and retrograde coarse-garnet schist; probably is the retrograde equivalent of charnockitic garnet-rich feldspathic quartz gneisses of the eastern Adirondacks. Locally contains mappable quartzite, garnet quartzite, calc-silicate gneiss, and marbles, mapped separately. Part of the aluminous schists and gneisses of the Washington Gneiss and Wilcox Formation and related rocks. Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Calc-silicate rock (Middle Mesoproterozoic) at surface, covers < 0.1 % of this area

Heterogeneous unit consists of dark-green hornblende-diopside rock or pale-green diopside rock; hornblende-calcite-diopside knotted rock; and rusty-weathering, beige scapolite-quartz-plagioclase gneiss, tremolite-phlogopite schist, and diopside quartzite. Part of the aluminous schists and gneisses of the Washington Gneiss and Wilcox Formation and related rocks. Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Netop Formation - phyllite and metasiltstone (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Predominantly light- to medium-gray and grayish-green phyllite and metasiltstone. The Netop Formation may be in part equivalent in age and facies to parts of the West Castleton and Hatch Hill Formations, but may extend lower and into the Neoproterozoic. Rocks of the Dorset Mountain slice (includes Dorset Mountain proper and Mount Equinox, southward to West Mountain near Bennington). Part of the Taconic Allochthon.

Waits River Formation - quartzite and feldspathic quartzite member (Lower Devonian and Upper Silurian) at surface, covers < 0.1 % of this area

Light-gray to tan, thinly bedded quartzite in beds 2 to 10 cm thick, exposed north of the Chester dome and south of Springfield; contains detrital zircon having Grenvillian provenance. Part of the Connecticut Valley Trough.

Tyson Formation - quartz phyllite member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Rusty-weathering, gray to grayish-green, chlorite-muscovite-quartz phyllite and minor beds of pebbly-quartz metawacke. Eastern and western flank of the Green Mountain massif.

Rowe Schist - garnet schist member (Cambrian and Neoproterozoic?) at surface, covers < 0.1 % of this area

Mainly yellowish-green, lustrous, biotite-chlorite-muscovite-plagioclase-quartz-garnet schist, distinguished by large garnets and coarse cross-biotite. Typical of rocks within the Stowe Formation elsewhere. Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks. Rowe Schist: Mapped in southern Vermont where the uppermost part is continuous with amphibolites, schists, and feldspathic schists of the Rowe Schist of Massachusetts. These upper units are continuous with rocks of the Stowe Formation to the north. Units in the middle and lowermost structural positions (above the Hoosac Formation) are in a similar structural position as rocks of the Ottauquechee and Pinney Hollow Formations, although structural continuity and correlations with the Ottauquechee and Pinney Hollow Formations are uncertain owing to extensive structural duplication by thrust faulting and folding.

Hoosac Formation - garnet biotite schist member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Medium-dark-gray to lustrous silvery-gray garnet-biotite-muscovite-plagioclase-quartz schist and feldspathic garnet schist; associated with CZhs member which it laterally replaces. Eastern flank of the Green Mountain massif and eastern domes.

Ottauquechee Formation - carbonaceous albite schist member (Cambrian) at surface, covers < 0.1 % of this area

Tan- to dark-gray-weathering, carbonaceous, medium- to coarse-grained chlorite-plagioclase-muscovite-quartz schist and interbedded tan, gray, and bluish-gray quartzite. Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks.

Tyson Formation - chlorite-muscovite phyllite and schist member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Pale-greenish-gray to yellowish-greenish-gray, chlorite-muscovite-quartz phyllite and schist; locally contains beds of pebbly metawacke and magnetite phyllite. Similar to but finer grained than the metawacke and phyllite member of the Pinnacle Formation (CZps). Eastern and western flank of the Green Mountain massif.

Granitic gneiss of Chittenden Intrusive Suite (?) (Late Mesoproterozoic) at surface, covers < 0.1 % of this area

Light-gray, coarse-grained, biotite-microcline megacrystic to even-grained granite gneiss closely associated with 1,149- to 1,120-Ma augen gneisses, in the northern part of the Green Mountain massif. Not distinguishable with certainty from older granitoids of the Stratton Mountain Intrusive Suite of the central and southern Green Mountains. Chittenden Intrusive Suite (1,149±8 Ma to 1,119±3 Ma). Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Ottauquechee Formation - feldspathic schist and granofels member (Cambrian) at surface, covers < 0.1 % of this area

Gray and grayish-green, biotite-chlorite-muscovite-albite-quartz schist or phyllite and granofels; contains coticule, locally richly garnetiferous. Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks.

Cavendish Formation - feldspathic schist and granofels member (Early Mesoproterozoic) at surface, covers < 0.1 % of this area

Light-gray to medium-dark-gray, rusty-weathering, white-plagioclase-spotted biotite-quartz-plagioclase granofels, massive grayish-green chlorite-spotted, magnetite-studded, biotite-plagioclase-quartz granofels and gneiss, and porphyroclastic plagioclase-augen-biotite mylonite gneiss. Unit less well-bedded than granofels of the Hoosac Formation and lacks amphibolites common in the Hoosac flanking the Chester and Athens domes. Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes. The term “Cavendish Formation” is restricted to two belts of rocks within the Chester dome; the larger belt occurs at Cavendish and on Hawks Mountain, and a less extensive belt, containing similar rocks, occurs near Star Hill. An Early Mesoproterozoic age is here favored for the Cavendish Formation on the basis of (1) the presence of deformed pegmatite (Y3Cp) and areas of Felchville Gneiss (Y1fg and Y1fga) within the Cavendish and (2) the marked resemblance of members of the Cavendish to aluminous and feldspathic schists, calc-silicate rocks, and quartzites within the Mount Holly Complex. Similarities to rocks of the Hoosac Formation are also striking and cannot be altogether dismissed; however, the Hoosac Formation lacks pegmatite and contains distinctive and well-bedded albitic granofels, mafic volcanics, and coarse pebble-to-cobble conglomerate, all absent from the Cavendish. Zircons from a quartzite lens in dolomite marble at locality 4 have Pb-Pb ages between 1,290 and 934 Ma and suggest some of the marble of the Cavendish may be younger than the Felchville Gneiss (Karabinos and others, 1999). Retrograded muscovite-rich, chlorite-spotted, chloritoid-bearing quartz phyllites and garnet granofels and other rocks of the Wilcox Formation (Y2wxs) closely resemble those of the Cavendish Formation, as do chloritic-muscovitic retrograded Y2rs members of the Mount Holly Complex in the Green Mountain massif. Dolomite marble, talc-tremolite rock, diopside quartzite, calc-silicate gneiss, and lustrous chlorite-spotted, chlorite-muscovite-rich retrograded garnet gneiss and schist in the Mount Holly Complex contain abundant pegmatite (Y3Cp) on Blue Ridge Mountain in Chittenden and are identical but lower-grade correlatives of the Cavendish Formation. The coarse garnet-staurolite- and kyanite-bearing Gassetts Schist Member is interpreted to be an Acadian remetamorphosed product of the retrograde aluminous rocks now seen throughout the Mount Holly Complex of the Green Mountain massif and in the Pine Hill area.

Ludlow Mountain granodiorite gneiss (Middle Mesoproterozoic) at surface, covers < 0.1 % of this area

Light-gray, medium- to fine-grained garnet-biotite-microcline-perthite granodiorite, magnetite-studded white aplite, and kyanite-tourmaline pegmatite. Contains 0.5-cm clots of muscovite possibly after beryl. Intrudes quartzite, lustrous schists (Y1rs), and calc-silicate rocks on Ludlow Mountain. U-Pb zircon SHRIMP age of 1,309±6 Ma, no. 9 (Aleinikoff and others, 2011). South Londonderry Igneous Suite (Middle and Early Mesoproterozoic) (1,393±9 Ma to 1,309±6 Ma). Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Branch Brook dike and sill complex - Williamsville facies (Ordovician and Late Cambrian) at surface, covers < 0.1 % of this area

Dark-gray to black, poorly layered, porphyritic and nonporphyritic ilmenite-epidote-chlorite-plagioclase-hornblende amphibolite. North River Igneous Suite (502±4 Ma to 471.4±3.7 Ma): collection of metatonalite, metatrondhjemite, and metabasalt occurring as intrusive dikes, sills, and small stocks, and possibly meta-andesite and metadacitic tuffs. Correlative with extrusive dacitic metavolcanic and meta-andesitic rocks of the Moretown and Cram Hill Formations. Coextensive in part with igneous rocks of the Hawley Formation of Massachusetts. Part of the Volcanic-arc intrusive and volcanic rocks of the North River Igneous Suite of the Rowe-Hawley zone. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Willoughby pluton - western zone (Devonian) at surface, covers < 0.1 % of this area

Light-gray to pink, medium- to very coarse grained, massive, miarolitic garnet-muscovite peraluminous leucogranite. Biotitic granodioritic western zone. Rb/Sr whole-rock age of 376±9 Ma (Ayuso and Arth, 1992). Igneous rocks of the Northeast Kingdom batholith of Ayuso and Arth (1992). Part of the New Hampshire Plutonic Suite.

Dalton Formation - lustrous quartz schist member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Dark-gray to silvery-gray, tourmaline-muscovite-biotite-quartz schist and feldspathic schist and quartzite. Occurs on eastern flank of the southern Green Mountain massif; similar in appearance to CZhs of the Hoosac Formation exposed to the east. Unit interfingers to the north with rocks of the Tyson Formation and to the east with rocks of the Hoosac Formation. Cover rocks of the Southern Green Mountains.

Providence Island Dolostone (Middle and Lower Ordovician) at surface, covers < 0.1 % of this area

Light-buff-tan- weathering, massive to thick-bedded, fine-grained dark-gray dolostone; has “beeswax-scored” surfaces; contains thin layers of fossiliferous bluish-gray limestone (largely equivalent to the Bridport Member of the Chipman Formation, north of Orwell). Part of the Beekmantown Group. Rocks of the Laurentian Margin. Part of the Adirondack lowlands and Lake Champlain lowlands (west of the Orwell and Champlain thrusts).

Cram Hill Formation - felsic and intermediate metavolcanic member (Middle? and Early Ordovician) at surface, covers < 0.1 % of this area

Occurs at different stratigraphic levels. Includes dark-gray and white layered metadacite and meta-andesite, gray- to tan-weathering blue-quartz phenocrystic metadacitic agglomerate, and grayish-green fragmental metadacitic and meta-andesite breccia. Similar to the volcanic agglomerate (Omwhv) within the Whetstone Hill Member of the Moretown Formation. A similar felsic layer interlayered within the Cram Hill Formation has a U-Pb zircon SHRIMP age of 483±3 Ma, no. 25 (Aleinikoff and others, 2011). Part of the metasedimentary host rocks of the North River Igneous Suite. Cram Hill Formation: western part of the Cram Hill Formation is in part correlative with Whetstone Hill Member of the Moretown Formation. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Chazy Group - undivided (Upper and Middle Ordovician) at surface, covers < 0.1 % of this area

Dark- to light-gray, massively bedded fossiliferous limestone and calcareous sandstone. Rocks of the Laurentian Margin. Part of the Adirondack lowlands and Lake Champlain lowlands (west of the Orwell and Champlain thrusts). Also part of the Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

Cram Hill Formation - amphibolite and greenstone member (Middle? and Early Ordovician) at surface, covers < 0.1 % of this area

Light-greenish-gray, feldspathic chlorite-actinolite greenstone and bedded andesitic to basaltic tuff and amphibolite, associated with ironstone, coticule, and minor pods of dolostone. Part of the metasedimentary host rocks of the North River Igneous Suite. Cram Hill Formation: western part of the Cram Hill Formation is in part correlative with Whetstone Hill Member of the Moretown Formation. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

College Hill Granite Gneiss (Middle Mesoproterozoic) at surface, covers < 0.1 % of this area

Light-gray to medium-dark-gray, porphyritic biotite-microcline-perthite granodioritic gneiss and pegmatite. Strongly deformed, lineated, and saturated with less deformed later pegmatite; grades outward into a migmatitic border exhibiting decreasing concentration of microcline megacrysts. Forms a single large intrusive mass on College Hill in Jamaica and west of Stratton Mountain; truncates structure in older gneisses. U-Pb zircon TIMS age of 1,244±8 Ma, no. 11 (Ratcliffe and others, 1991; Aleinikoff and others, 2011). Stratton Mountain Intrusive Suite (Middle Mesoproterozoic) (1,244±8 Ma to 1,221±4 Ma). Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Comerford Intrusive Complex - metatholeiitic mafic dikes (Late Silurian) at surface, covers < 0.1 % of this area

Abundant, foliated to weakly foliated, metatholeiitic mafic dikes; some sheeted. Shown as overprint. Part of the Lake Memphremagog Intrusive Suite (425±3 Ma to 418.5±2 Ma).

Rowe Schist - Cooper Hill member (Cambrian and Neoproterozoic?) at surface, covers < 0.1 % of this area

Dark-gray or green, dull-gray- and rusty-weathering, slabby, well-foliated, quartz-rich muscovite-biotite-plagioclase-quartz schist, garnet schist, and splintery chlorite-chloritoid-muscovite-plagioclase (±garnet)-quartz schist, with minor feldspathic biotite gneiss. Unit noncarbonaceous and atypical of the Ottauquechee Formation except for minor layers of carbonaceous schist (CZrc). Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks. Rowe Schist: Mapped in southern Vermont where the uppermost part is continuous with amphibolites, schists, and feldspathic schists of the Rowe Schist of Massachusetts. These upper units are continuous with rocks of the Stowe Formation to the north. Units in the middle and lowermost structural positions (above the Hoosac Formation) are in a similar structural position as rocks of the Ottauquechee and Pinney Hollow Formations, although structural continuity and correlations with the Ottauquechee and Pinney Hollow Formations are uncertain owing to extensive structural duplication by thrust faulting and folding.

Cram Hill Formation - phyllite-chip conglomerate and slate conglomerate member (Middle? and Early Ordovician) at surface, covers < 0.1 % of this area

Dark-gray, carbonaceous garnet-pyrite-sericite-chlorite-quartz phyllite with clasts of siltstone, phyllite, quartzite, and dark-gray slate breccia interbedded with Coburn Hill Metabasalt Member (Ochcv). Unit correlative with the St. Daniel Group of Québec. Part of the Cram Hill Formation of the Newport Center area. Part of the metasedimentary host rocks of the North River Igneous Suite. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Hazens Notch Formation - greenstone and amphibolite member (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Dark-green, pitted-weathering, foliated mafic schist to massive greenstone containing varying amounts of chlorite, albite, carbonate, epidote, amphibole, and sphene; and amphibolite containing varying amounts of hornblende, actinolite, albite, chlorite, epidote, biotite, magnetite, and sphene. Cover rocks north of the Lincoln Mountain massif.

Plymouth Formation - feldspathic quartzite member (Cambrian) at surface, covers < 0.1 % of this area

Thinly laminated but massive-appearing, gray- and brownish-gray- to tan-weathering flaggy biotite-muscovite feldspathic quartzite and phyllitic quartzite. Resembles feldspathic quartzite of the Dalton Formation (CZdfq) and similar quartzite of the Moosalamoo Formation (CZmf) above the Forestdale Formation. Eastern flank of the Green Mountain massif and eastern domes.

Dalton Formation - feldspathic quartzite member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Light-tan to gray-weathering, massive to thin-bedded, flaggy, tourmaline-muscovite-feldspar quartzite and interbedded phyllitic quartzite. Unit interfingers to the north with rocks of the Tyson Formation and to the east with rocks of the Hoosac Formation. Cover rocks of the Southern Green Mountains.

Monadnock Mountain pluton - quartz syenite (Middle Jurassic) at surface, covers < 0.1 % of this area

Greenish-gray to pink hornblende-biotite quartz syenite. Monadnock Mountain pluton: Composite stock of quartz syenite, syenite granite, and essexite. K-Ar age of 175±4 Ma (Foland and Faul, 1977). Part of the White Mountain Igneous Suite.

Oliverian Plutonic Suite - granodioritic to quartz dioritic gneissic (Late Ordovician) at surface, covers < 0.1 % of this area

Granodioritic to quartz dioritic gneissic border phase of Oobg, perhaps in part metasomatic. Part of the Bronson Hill arch intrusive rocks.

Amphibolite (Early Mesoproterozoic) at surface, covers < 0.1 % of this area

Dark-grayish-green, fine-grained quartz-hornblende-plagioclase amphibolite, locally garnetiferous, and medium-grained hornblende-plagioclase amphibolite. Occurs with belts of calc-silicate rocks and as lenses within biotite-quartz-plagioclase paragneiss. Unit probably includes both meta-igneous and metasedimentary rocks intercalated throughout the Early and Middle Mesoproterozoic-age rocks of the Mount Holly Complex. Part of the aluminous schists and gneisses of the Washington Gneiss and Wilcox Formation and related rocks. Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Moosalamoo Formation - gray phyllite and metawacke member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Dark-gray, sooty-weathering, splintery sulfidic to non-sulfidic quartz phyllite and pebbly and gritty biotite metawacke. Cover rocks of the Lincoln Mountain massif and northwestern flank of the Green Mountain massif.

Stowe Formation - large-garnet schist member (Cambrian and Neoproterozoic?) at surface, covers < 0.1 % of this area

Silvery-green to grayish-green, garnet (large)- plagioclase-biotite (chlorite)-quartz-muscovite schist. Comparable to garnet schist member of the Rowe Schist in southern Vermont and around the Chester and Athens domes (CZrgs). Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks.

Dalton Formation - conglomerate member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Commonly tan- to yellowish-tan-weathering, coarse- to fine-grained quartz-pebble to -cobble, quartz conglomerate and schistose quartz conglomerate. Locally dark-gray biotite-muscovite-blue-quartz-pebble wacke to conglomerate. Occurs at or near base of unit. Unit interfingers to the north with rocks of the Tyson Formation and to the east with rocks of the Hoosac Formation. Cover rocks of the Southern Green Mountains.

Sweetsburg Formation (Lower Ordovician and Cambrian?) at surface, covers < 0.1 % of this area

Black to gray, graphitic, quartzose phyllite and schist, with tan-weathering layers and pods of gray dolostone and black quartzite. Cover rocks of the Saint Albans area.

Hazens Notch Formation - schist member (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Rusty-weathering, non-graphitic, sulfidic chlorite-muscovite-quartz schist. Cover rocks north of the Lincoln Mountain massif.

Ironbound Mountain Formation - rhythmically graded member (Lower Devonian) at surface, covers < 0.1 % of this area

Light- to medium-gray, fine-grained micaceous metasandstones that grade upward into subordinate dark-gray slate or phyllite; some rocks are calcareous. Graded sets range in thickness from a few centimeters to about a meter; typically they are 10 to 30 cm thick. Contact with Di gradational. Part of the Connecticut Valley Trough.

Cumberland Head Formation (Upper Ordovician) at surface, covers < 0.1 % of this area

Interbedded graded bioclastic limestone, bluish-gray calcareous shale, and laminated shale. Rocks of the Laurentian Margin. Part of the Adirondack lowlands and Lake Champlain lowlands (west of the Orwell and Champlain thrusts).

Ottauquechee Formation - schist and quartzite member (Cambrian) at surface, covers < 0.1 % of this area

Light-gray to tan, rusty-weathering, laminated sandy muscovite-plagioclase-quartz schist and tan quartzite. Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks.

Rowe Schist - biotite-plagioclase schist and gneiss member (Cambrian and Neoproterozoic?) at surface, covers < 0.1 % of this area

Gray and light-gray-weathering, medium- to coarse-grained biotite-plagioclase-sericite-quartz schist and gneiss, commonly flecked with large cross-biotite. Locally contains coarse garnet. Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks. Rowe Schist: Mapped in southern Vermont where the uppermost part is continuous with amphibolites, schists, and feldspathic schists of the Rowe Schist of Massachusetts. These upper units are continuous with rocks of the Stowe Formation to the north. Units in the middle and lowermost structural positions (above the Hoosac Formation) are in a similar structural position as rocks of the Ottauquechee and Pinney Hollow Formations, although structural continuity and correlations with the Ottauquechee and Pinney Hollow Formations are uncertain owing to extensive structural duplication by thrust faulting and folding.

Underhill Formation - quartz-laminated schist member (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Light-gray to tan and rusty-weathering, fine-grained, well-foliated mylonitic albite-chlorite-muscovite-quartz (±dolomite)-laminated schist. Cover rocks north of the Lincoln Mountain massif.

Cram Hill Formation - phyllite and quartzite member (Middle? and Early Ordovician) at surface, covers < 0.1 % of this area

Light-gray to tan, rusty-weathering, fine- grained quartz-sericite-chlorite-albite phyllite, quartzite, and flinty sulfidic granofels; thin layers of felsite, conglomerate, and breccia occur in the vicinity of Coburn Hill. Paper schist fabric occurs locally on the west side of Coburn Hill. Part of the Cram Hill Formation of the Newport Center area. Part of the metasedimentary host rocks of the North River Igneous Suite. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Ammonoosuc Volcanics of Billings (1935) - metarhyolite tuff, lapilli tuff, tuff breccia, and lava (Upper and Middle Ordovician) at surface, covers < 0.1 % of this area

Greenish-gray, light-bluish-gray, or medium-bluish-gray metarhyolite tuff, lapilli tuff, tuff breccia, and lava. Generally porphyritic with 5 to 20 percent plagioclase and, in some places, quartz phenocrysts. Generally strongly foliated with waxy sheen on foliation surfaces. Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt.

Ascutney Mountain stock – syenite (Early Cretaceous) at surface, covers < 0.1 % of this area

Syenite-porphyrite to sericite-perthite-hornblende-biotite syenite; contains minor fayalite, augite, and quartz; occurs as a partial ring dike in the Little Ascutney stock. Part of the White Mountain Igneous Suite; Ascutney Mountain igneous complex - Consists of two plutons, a partial ring dike, and screens of volcanic rocks. K-Ar ages of 122 to 120 Ma (Foland and Faul, 1977).

Hoosac Formation - chlorite albite schist and granofels member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Pale-green to light-greenish-gray, chlorite-magnetite-white-albite-spotted-quartz granofels and schist. Eastern flank of the Green Mountain massif and eastern domes.

Littleton Formation (Lower Devonian) at surface, covers < 0.1 % of this area

Medium-dark- to dark-gray slate interlayered with light-gray, fine-grained micaceous quartzite; in southeastern Vermont near the Vernon dome Dl is equated with DSwb and may be older than in the Bradford area. Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt.

Valcour Formation (Upper Ordovician) at surface, covers < 0.1 % of this area

Dark- to light-gray fossiliferous limestone. Part of the Chazy Group. Rocks of the Laurentian Margin. Part of the Adirondack lowlands and Lake Champlain lowlands (west of the Orwell and Champlain thrusts). Also part of the Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

Waits River Formation - felsic volcanic member (Lower Devonian and Upper Silurian) at surface, covers < 0.1 % of this area

Light-gray to grayish-green, chlorite-biotite-muscovite-plagioclase-quartz schist and fragmental quartz-plagioclase granofels or metatuff. In Springfield, contains a dated metafelsite layer interpreted as a dike cutting the Standing Pond Volcanics, that yielded a U-Pb zircon TIMS age of 423±4 Ma, no. 32 (Aleinikoff and Karabinos, 1990; Hueber and others, 1990). Part of the Connecticut Valley Trough.

Stowe Formation - amphibolite and greenstone member (Cambrian and Neoproterozoic?) at surface, covers < 0.1 % of this area

Dark-green hornblende-rich biotite-plagioclase (±garnet) amphibolite, epidote-hornblende-plagioclase-quartz amphibolite, and light-grayish-green, rusty-weathering, carbonate-pitted ankerite-magnetite-albite-epidote (plagioclase) feldspathic greenstone and interbedded feldspathic quartzite (CZsg). Locally a mafic basaltic metawacke and interbedded amphibolite. Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks.

Pinnacle Formation - amphibolitic greenstone member (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Calcite-biotite-sphene-albite-actinolite-epidote-chlorite greenstone with dark-green porphyroblasts of actinolitic hornblende. Cover rocks of the Lincoln Mountain massif and northwestern flank of the Green Mountain massif.

Cram Hill Formation - phyllite member (Middle? and Early Ordovician) at surface, covers < 0.1 % of this area

Gray to silvery-green, sericite-chlorite-quartz phyllite with thin beds of rusty-weathering, pearly-white, fine-grained granofels. Interlayered with Ochuc and Ochsb at the contacts. Mapped locally in the Albany area. Part of the Cram Hill Formation of the Newport Center area. Part of the metasedimentary host rocks of the North River Igneous Suite. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Ammonoosuc Volcanics of Billings (1935) - metasiltstone and phyllite (Upper and Middle Ordovician) at surface, covers < 0.1 % of this area

Medium-light-bluish-gray, medium-bluish-gray, medium-dark-gray, to medium-dark-greenish-gray metasiltstone and phyllite, and medium-gray feldspathic metawacke. Purple tinge common; coticule and magnetite locally abundant. Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt.

Chipman Formation - Burchards Member (Middle Ordovician) at surface, covers < 0.1 % of this area

Light-bluish-gray mottled dolomitic limestone. Chipman Formation (mapped south of Wings Point). Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

Tonalite gneiss (Early Mesoproterozoic) at surface, covers < 0.1 % of this area

Medium-gray- to light-gray-weathering, biotite (±hornblende) tonalite gneiss exposed on Torment Hill in Weston; probably correlative with the Baileys Mills tonalitic gneiss or the Felchville trondhjemite facies (Y1fg) of the Chester dome, but undated. South Londonderry Igneous Suite (Middle and Early Mesoproterozoic) (1,393±9 Ma to 1,309±6 Ma). Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Black River Group - undivided (Upper Ordovician) at surface, covers < 0.1 % of this area

Thin-bedded to massive dolostone, sandy dolostone, and light-gray limestone; vertical burrows in basal beds; upper beds fossiliferous with black chert. Rocks of the Laurentian Margin. Part of the Adirondack lowlands and Lake Champlain lowlands (west of the Orwell and Champlain thrusts).

Stamford Granite - aplitic granite (Neoproterozoic) at surface, covers < 0.1 % of this area

A fine-grained facies consisting of white-weathering, muscovite-biotite-microcline-plagioclase aplitic granite locally forms a border facies or thin internal dikes. U-Pb zircon upper-intercept age of 962±1 Ma, no. 20 (revised from Karabinos and Aleinikoff, 1990). Cardinal Brook Intrusive Suite (965±4 Ma to 945±7 Ma). Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Ottauquechee Formation - amphibolite and greenstone member (Cambrian) at surface, covers < 0.1 % of this area

Dark-green plagioclase-hornblende (±quartz) amphibolite and rusty-pale-green, punky-weathering ankeritic-chloritic greenstone. Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks.

Tillotson Peak Structural Complex (Cambrian) at surface, covers < 0.1 % of this area

Mafic schist and amphibolite unit. Dark-bluish-gray, fine- to medium-grained, massive to foliated blueschist composed of amphibole (glaucophane, barroisite, and actinolite), epidote, garnet, chlorite with minor magnetite, pyrite, and apatite. Quartz and garnet coticule occur locally. Eclogite occurs locally, delimited by green, medium-grained layers and pods of garnet, omphacite, glaucophane, epidote, quartz, albite, and white mica. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Cram Hill Formation - Umbrella Hill Conglomerate member (Middle? and Early Ordovician) at surface, covers < 0.1 % of this area

Quartz-pebble and phyllitic-fragment conglomerate, and tan to gray phyllite. Occurs as lenses, locally unconformable with the underlying Stowe Formation at Umbrella Hill; occurs at different stratigraphic levels in the Cram Hill Formation north of Albany. Interbedded with Coburn Hill Metabasalt Member (Ochcv) and phyllite-chip conglomerate and slate conglomerate member (Ochsb) north of Albany. Part of the Cram Hill Formation of the Newport Center area. Part of the metasedimentary host rocks of the North River Igneous Suite. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Pegmatite (Late Mesoproterozoic) at surface, covers < 0.1 % of this area

Light-gray to pinkish-gray, biotite-muscovite (±garnet±tourmaline±magnetite) granite pegmatite as crosscutting pods and larger bodies. Albitic garnet-muscovite pegmatite common in metapelitic rocks of the Mount Holly Complex, and especially prominent in the northern and east-central parts of the Green Mountain massif. Assignment of individual pegmatites to Y3C is highly interpretive based on crosscutting of gneissosity and weakly deformed character. Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Waits River Formation - Crow Hill Member of Hall (1959) (Lower Devonian and Upper Silurian) at surface, covers < 0.1 % of this area

Gray quartzite and feldspathic quartzite, in part volcaniclastic and locally interbedded with amphibolite. Part of the Connecticut Valley Trough.

Moretown Formation - Harlow Bridge quartzite member (Lower Ordovician to Cambrian?) at surface, covers < 0.1 % of this area

Buff-weathering, tan to green, fine-grained massive to thinly bedded quartzite intercalated with green phyllite and schist. Part of the metasedimentary host rocks of the North River Igneous Suite. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Waits River Formation - Garbenschiefer member (Lower Devonian and Upper Silurian) at surface, covers < 0.1 % of this area

Rusty-brown to silvery-gray, coarse-grained, garnet (large)-muscovite-biotite-hornblende schist and hornblende-fascicule schist. Part of the Connecticut Valley Trough.

Pharaoh Mountain Gneiss of Wiener and others (1984) (Late to Middle Mesoproterozoic) at surface, covers < 0.1 % of this area

Rusty-grayish-brown- to brown-weathering, knubbly coarse-grained magnetite-garnet-hornblende and pyroxene-bearing charnockitic gneiss and garnet-hornblende granite gneiss. Has large polycrystalline aggregates of plagioclase as much as 1.5 cm long, recrystallized from pre-Ottawan phenocrysts (?) of plagioclase. Contains mappable and folded screens of marble, calc-silicate rock (Y2cs), mafic diopside-hypersthene gneiss, and interbedded sillimanite-garnet quartzite (Y2qz). Interpreted as largely intrusive but may contain some charnockitic gneiss of uncertain origin. Rocks of the Adirondacks in Vermont and in the Whitehall, N.Y., area.

East Barre plutons (Devonian) at surface, covers < 0.1 % of this area

Gray, homogeneous, fine- to medium-grained muscovite-biotite granodiorite. U-Pb zircon Sensitive High Resolution Ion Microprobe (SHRIMP) age of 368±4 Ma, no. 47 (Aleinikoff and others, 2011). Part of other plutons of the New Hampshire Plutonic Suite.

Okemo Quartzite (Middle Mesoproterozoic) at surface, covers < 0.1 % of this area

Light-tan to whitish-gray, massive vitreous quartzite in beds several meters thick, interlayered with rusty-grayish-brown garnet-muscovitic quartzite and aluminous sericite-muscovite-tourmaline retrograde phyllite. Occurs as a thick unit on Ludlow Mountain, in Okemo State Forest. U-Pb ages of detrital zircons range from 1,359±32 Ma to 1,261±62 Ma, no. 10 (Aleinikoff and others, 2011), and suggest derivation from trondhjemitic gneiss of the South Londonderry Igneous Suite. Part of the aluminous schists and gneisses of the Washington Gneiss and Wilcox Formation and related rocks. Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Great Meadows Formation - dolostone (Lower Ordovician) at surface, covers < 0.1 % of this area

Light-gray, medium-grained, medium- to thick-bedded dolostone, locally cherty. Part of the Beekmantown Group. Rocks of the Laurentian Margin. Part of the Adirondack lowlands and Lake Champlain lowlands (west of the Orwell and Champlain thrusts).

Tyson Formation - conglomerate member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Massive to well-bedded chlorite-biotite (±albite)-quartz-pebble, -cobble, and -boulder conglomerate, feldspathic conglomeratic metawacke, and locally a dolomite-cemented feldspathic quartz-pebble conglomerate. Occurs at base and in lower part of the Tyson Formation. Eastern and western flank of the Green Mountain massif.

Microcline-magnetite augen gneiss at Brandon Gap (Late Mesoproterozoic) at surface, covers < 0.1 % of this area

Pinkish-gray to medium-dark-gray, biotite-magnetite-microcline-plagioclase augen gneiss. U-Pb zircon SHRIMP age of 1,149±8 Ma, no. 13 (Aleinikoff and others, 2011). Unit is associated with minor exposures of metadiorite to tonalitic gneisses; crosscuts a gneissosity in country rocks and may extend northward along eastern limb of Lincoln Mountain massif as unit Y3Ama. Chittenden Intrusive Suite (1,149±8 Ma to 1,119±3 Ma). Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Underhill Formation - greenstone and amphibolite member (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Thinly bedded carbonate-albite-epidote greenstone and massive magnetite-albite-amphibole-biotite-epidote amphibolite; light- to dark-green, fine- to medium-grained epidote-chlorite albite-amphibole schist; dark-green, coarse-grained, weakly foliated epidote-biotite-albite-amphibole amphibolite. Cover rocks north of the Lincoln Mountain massif.

Netop Formation - wacke member (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Bluish-gray, fine-grained metawacke and metasiltstone, perhaps equivalent to the Bomoseen Graywacke Member of the Bull Formation. Rocks of the Dorset Mountain slice (includes Dorset Mountain proper and Mount Equinox, southward to West Mountain near Bennington). Part of the Taconic Allochthon.

Fort Cassin Formation (Middle and Lower Ordovician) at surface, covers < 0.1 % of this area

Shown locally from Whitehall, N.Y., to Orwell, Vt. Laterally equivalent to Providence Island Dolostone. Part of the Beekmantown Group. Rocks of the Laurentian Margin. Part of the Adirondack lowlands and Lake Champlain lowlands (west of the Orwell and Champlain thrusts).

Little Ascutney stock - gabbro and diorite (Early Cretaceous) at surface, covers < 0.1 % of this area

Medium- to coarse-grained augite-hornblende-biotite gabbro infiltrated by hornblende and biotite diorite. Part of the White Mountain Igneous Suite; Little Ascutney stock: A composite gabbro-diorite stock having two (eastern and western) intrusive centers defined by weakly developed igneous foliation. Gabbro is intruded by abundant, poorly defined areas of diorite. Includes two areas of syenite (Kas).

Tyson Formation - undivided (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Phyllite and metawacke. Shown east of Rutland. Eastern and western flank of the Green Mountain massif.

Bull Formation - Zion Hill Quartzite member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Light-greenish-gray to whitish-gray-weathering, massive vitreous quartzite; locally contains quartz-pebble conglomerate and wacke near the base. Unit commonly 5 to 10 m thick but is as much as 65 m thick; occurs as many lenticular quartzites within the Mettawee slate facies in the Bull Formation, not restricted to one horizon. Rocks of the Giddings Brook, Sunset Lake, and Bird Mountain slices. Part of the Taconic Allochthon.

Sawyer Mountain Formation (Devonian and Silurian) at surface, covers < 0.1 % of this area

Greenish-gray to dark-gray, pyritic, locally calcareous phyllite and light-gray, locally pyritic and calcareous, fine- to medium-grained, feldspar-rich metasandstone; some beds punky weathering. Graded grit and conglomerate beds (having cobble-size clasts of quartz and felsite) toward base. Interpreted as transitional between Connecticut Valley and Bronson Hill sequences and correlative with Frontenac Formation. Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt.

Tyson Formation - albite schist member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Dark-gray to black, locally carbonaceous, rusty-brown-weathering biotite-rich quartz schist and dark biotite-albite schist. Eastern and western flank of the Green Mountain massif.

Tyson Formation - dolostone member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Largely massive, gray-, beige-, and pinkish-gray-weathering dolostone, beds of pebbly quartz dolostone, and pink- to orange-tan-weathering dolostone as lenses in phyllite. Contains beds of bluish-gray and whitish-gray vitreous quartzite. Similar to dolostone of the Forestdale Formation (CZfd). Eastern and western flank of the Green Mountain massif.

Great Meadows Formation - Winchell Creek Member (Lower Ordovician) at surface, covers < 0.1 % of this area

Tan-weathering, gray, well-bedded and crossbedded laminated quartzite and dolostone; sandy beds weather to a woody-grained surface texture. Part of the Beekmantown Group. Rocks of the Laurentian Margin. Part of the Adirondack lowlands and Lake Champlain lowlands (west of the Orwell and Champlain thrusts).

Moretown Formation - Whetstone Hill Member - metavolcanic facies (Lower Ordovician to Cambrian?) at surface, covers < 0.1 % of this area

Pale-tannish-gray- to purplish-gray-weathering, phyllitic metadacitic volcanic breccia, agglomerate, and grayish-green fragmental meta-andesitic breccia; may occur at several levels. Part of the metasedimentary host rocks of the North River Igneous Suite. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Ticonderoga Formation (Upper Cambrian) at surface, covers < 0.1 % of this area

Light-gray, yellowish-gray- to buff- weathering quartzose dolostone, pebbly dolomitic quartzite, and interbedded quartzite. Part of the Beekmantown Group. Rocks of the Laurentian Margin. Part of the Adirondack lowlands and Lake Champlain lowlands (west of the Orwell and Champlain thrusts).

Cram Hill Formation - granofels member (Middle? and Early Ordovician) at surface, covers < 0.1 % of this area

Dark-medium-gray biotite-plagioclase-quartz granofels and grayish-green chlorite-plagioclase-quartz granofels; contains thin layers of ankerite-epidote greenstone, ankerite-spotted feldspathic granofels, and coticule. Locally hornblende rich at higher metamorphic grade. Part of the metasedimentary host rocks of the North River Igneous Suite. Cram Hill Formation: western part of the Cram Hill Formation is in part correlative with Whetstone Hill Member of the Moretown Formation. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Underhill Formation - quartzite, granofels, and metawacke (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Local lenses of white to pale-gray quartzite, quartz-albite granofels, quartz-granule chlorite (±biotite) metawacke. Cover rocks north of the Lincoln Mountain massif.

Pinnacle Formation - calcareous greenstone member (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Rusty-weathering and pitted, dark-green greenstone with laminae and splotches of calcareous material; locally interbedded with calcareous metagraywacke. Cover rocks of the Lincoln Mountain massif and northwestern flank of the Green Mountain massif.

Washburn Brook Formation - siltstone, quartzite, volcanogenic chert, and ironstone (Upper and Middle Ordovician) at surface, covers < 0.1 % of this area

Metamorphosed gray siltstone, quartzite, volcanogenic chert, and ironstone, all typically containing coticule and magnetite. Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt.

Rawsonville trondhjemite gneiss - aplite (Early Mesoproterozoic) at surface, covers < 0.1 % of this area

Chalky-white to light-gray-weathering, medium- to coarse-grained aplite. Dated sample with U-Pb zircon SHRIMP age of 1,367±16 Ma, no. 3 (Ratcliffe and others, 1991; Aleinikoff and others, 2011) from crest of Bromley Mountain; U-Pb zircon age of 1,348±3 Ma, no. 6 (Ratcliffe and others, 1991). South Londonderry Igneous Suite (Middle and Early Mesoproterozoic) (1,393±9 Ma to 1,309±6 Ma). Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Fairlee Quartz Monzonite (Early Devonian) at surface, covers < 0.1 % of this area

Greenish-gray, pink-tinged, weakly foliated, coarse-grained to porphyritic biotite granite of the Fairlee pluton. U-Pb zircon age of 410±5 Ma, no. 42 (Moench and Aleinikoff, 2003). Part of the Bronson Hill arch intrusive rocks.

Rowe Schist - chlorite schist member (Cambrian and Neoproterozoic?) at surface, covers < 0.1 % of this area

Rusty-gray- to yellowish-brown-weathering, lustrous, non-carbonaceous, well-foliated chlorite-quartz-muscovite (±plagioclase) schist. Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks. Rowe Schist: Mapped in southern Vermont where the uppermost part is continuous with amphibolites, schists, and feldspathic schists of the Rowe Schist of Massachusetts. These upper units are continuous with rocks of the Stowe Formation to the north. Units in the middle and lowermost structural positions (above the Hoosac Formation) are in a similar structural position as rocks of the Ottauquechee and Pinney Hollow Formations, although structural continuity and correlations with the Ottauquechee and Pinney Hollow Formations are uncertain owing to extensive structural duplication by thrust faulting and folding.

White Brook Formation (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Buff to cream-colored massive dolomite and dolomitic sandstone, containing prominent zone of massive and specular hematite near top at Sheldon. Cover rocks north of the Lincoln Mountain massif.

Moretown Formation - granofels and coticule member (Lower Ordovician to Cambrian?) at surface, covers < 0.1 % of this area

Grayish-green, chlorite-biotite-plagioclase-quartz granofels and schist containing abundant fine layers of pinkish-gray small-garnet quartzite and coticule. Part of the metasedimentary host rocks of the North River Igneous Suite. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Nassau Formation of Potter (1972) - Bomoseen Member (Neoproterozoic) at surface, covers < 0.1 % of this area

Pale-reddish-brown to light-gray-weathering, medium- and fine-grained, massive to thickly bedded, olive-green to gray micaceous quartz-feldspar graywacke and siltstone, locally containing coarse detrital muscovite, biotite, and autoclastic slate chips. Resembles finer grained parts of the Rensselaer Graywacke Member of the Nassau Formation (of Potter, 1972), and the Bird Mountain Grit (of Dale, 1900). Unit interfingers with and grades laterally into the Mettawee slate facies. In the Mt. Anthony area is shown as CZnb (Bomoseen Member of the Nassau Formation of Potter, 1972). Rocks of the Giddings Brook, Sunset Lake, and Bird Mountain slices. Part of the Taconic Allochthon.

Cole Pond tonalite gneiss (Middle Mesoproterozoic) at surface, covers < 0.1 % of this area

Gray to medium-dark-gray, biotite-rich metatonalite gneiss, having irregular screens, and xenoliths of more mafic hornblende-biotite tonalite or diorite gneiss. U-Pb zircon SHRIMP age of 1,321±9 Ma, no. 7 (Ratcliffe and others, 1991; Aleinikoff and others, 2011). South Londonderry Igneous Suite (Middle and Early Mesoproterozoic) (1,393±9 Ma to 1,309±6 Ma). Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Parker Slate - dolostone member (Cambrian) at surface, covers < 0.1 % of this area

Massive beds of white to buff dolostone. Cover rocks of the Saint Albans area.

Waits River Formation - muscovite porphyroblastic carbonaceous schist member (Lower Devonian and Upper Silurian) at surface, covers < 0.1 % of this area

Dark-gray to coaly-black, fine-grained plagioclase-muscovite-quartz schist and metawacke, shown southeast of Springfield; in part correlative with staurolite-grade rocks mapped as Littleton Formation (Dl) flanking the Vernon dome (shown as DSwb/Dl). Part of the Connecticut Valley Trough.

Day Point Formation (Middle Ordovician) at surface, covers < 0.1 % of this area

Gray, thin-bedded to massive sandstone and fossiliferous limestone. Part of the Chazy Group. Rocks of the Laurentian Margin. Part of the Adirondack lowlands and Lake Champlain lowlands (west of the Orwell and Champlain thrusts). Also part of the Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

Gorge Formation (Lower Ordovician and Cambrian) at surface, covers < 0.1 % of this area

Dolomite, and dolomite breccia composed of angular clasts of dolostone, sandstone, and chert in a buff to gray quartzose dolostone. Cover rocks of the Saint Albans area.

Northfield Formation - quartzose limestone (Lower Devonian and Upper Silurian) at surface, covers < 0.1 % of this area

Beds of quartzose limestone. Part of the Connecticut Valley Trough.

Pinney Hollow Formation - black phyllite member (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Dark-gray to black, sulfidic biotite-plagioclase-quartz schist, commonly interbedded with or adjacent to amphibolite and greenstone member (CZpha); locally is a silvery-gray sulfidic biotite phyllite. Cover rocks of Green Mountain anticlinorium.

Belvidere Mountain Structural Complex - mafic schist (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Green, fine-grained schist composed of chlorite, actinolite, albite, and epidote with biotite, calcite, sericite, quartz, sphene, pyrite, and magnetite; includes homogeneous schistose greenstone, albitic greenstone, and massive banded greenstone. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Newport Intrusive Complex - diorite and trondhjemite (Late Silurian) at surface, covers < 0.1 % of this area

Metamorphosed diorite, trondhjemite, and diabase, consisting of massive to foliated, light-gray to grayish-green, chalky-weathering diorite with xenoliths of green phyllite and trondhjemite; and massive, tan-weathering, medium- to coarse-grained trondhjemite with xenoliths of diabase. Numerous crosscutting quartz-feldspar veinlets show in relief on the weathering surface. Unit intrudes Cram Hill Formation. U-Pb zircon SHRIMP age of 425±3 Ma, no. 39 (Aleinikoff and others, 2011). Part of the Lake Memphremagog Intrusive Suite (425±3 Ma to 418.5±2 Ma).

Pinnacle Formation - feldspathic greenstone member (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Olive-drab-weathering, dark-green, fine-grained greenstone with remnant plagioclase feldspar phenocrysts up to 1.5 cm in diameter. Cover rocks of the Lincoln Mountain massif and northwestern flank of the Green Mountain massif.

Moretown Formation - carbonaceous schist member (Lower Ordovician to Cambrian?) at surface, covers < 0.1 % of this area

Dark-gray, fine-grained carbonaceous biotite-muscovite-quartz (±garnet) phyllite and schist. Occurs west of Montpelier. Part of the metasedimentary host rocks of the North River Igneous Suite. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Dalton Formation - quartzite member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Tan to whitish-gray vitreous quartzite and minor blue-quartz-pebble quartzite. Unit interfingers to the north with rocks of the Tyson Formation and to the east with rocks of the Hoosac Formation. Cover rocks of the Southern Green Mountains.

West Bridgewater Formation - dark-gray and green phyllite member (Middle Ordovician) at surface, covers < 0.1 % of this area

Interbedded dark-gray and grayish-green chlorite-muscovite-quartz-knotted albitic phyllite, containing pods of bluish-gray dolostone. (Correlation with West Bridgewater Formation uncertain.) Mapped only in the area west of Granville. Cover rocks north of the Lincoln Mountain massif.

Moretown Formation - Whetstone Hill Member - black sulfidic carbonaceous schist facies (Lower Ordovician to Cambrian?) at surface, covers < 0.1 % of this area

Dark-gray, sooty- and rusty-weathering, sulfidic biotite-muscovite-plagioclase-quartz schist and granofels; is a lateral variant of Omwh. Contains layers of rusty-weathering amphibolite and dark-gray quartzite. Part of the metasedimentary host rocks of the North River Igneous Suite. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Biotite granite gneiss at Baker Brook (Mesoproterozoic) at surface, covers < 0.1 % of this area

Undated light-gray biotite granite gneiss containing abundant rose-colored zircon also is confined to the Pine Hill slice. Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Ludlow Mountain aplitic gneiss (Middle Mesoproterozoic) at surface, covers < 0.1 % of this area

Light-gray to white, very fine grained microcline-plagioclase-quartz (±magnetite) aplitic gneiss; contains sparing amounts of biotite, and secondary muscovite. Unit interpreted to be border facies of Y2lgg. Y2ap is similar aplitic gneiss, but is not in contact with either Y2lgg or Y2phg. Exposed on Ludlow Mountain. South Londonderry Igneous Suite (Middle and Early Mesoproterozoic) (1,393±9 Ma to 1,309±6 Ma). Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Bird Mountain Grit of Dale (1900) (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Dark-gray to greenish-gray and whitish-gray, massive chlorite-quartz wacke, pebble conglomerate, and purplish-gray hematitic lithic wacke. Unit is rich in fragmental plagioclase, phosphatic nodules, fragments of gray quartzite, and purple and green slate chips. Interpreted as a coarse-grained variant of part of the Zion Hill Quartzite Member, well exposed in and around Bird Mountain. Unit resembles in stratigraphic position and lithology the Rensselaer Graywacke Member of the Nassau Formation (of Potter, 1972) in the Bennington area (CZnr). Rocks of the Giddings Brook, Sunset Lake, and Bird Mountain slices. Part of the Taconic Allochthon.

Shaw Mountain Formation (Upper to Lower Silurian) at surface, covers < 0.1 % of this area

White to yellowish-gray quartz-pebble conglomerate and conglomeratic quartzite, having clasts of milky-white quartz as much as 2.5 cm in diameter in a white to tan quartzite matrix, in beds 0.5 to 1 m thick; and yellowish-gray to light-gray phyllitic quartzite, quartz-pebble to -granule phyllite, and steel-gray to tan vitreous quartzite in beds as much as 5 m thick. Part of the Connecticut Valley Trough.

Black Mountain pluton of the Guilford dome (Devonian) at surface, covers < 0.1 % of this area

Weakly foliated, light-gray to whitish-gray, garnet-biotite-muscovite granite, minor pegmatite, and aplite dikes (Dg). Rb/Sr muscovite age of 383±7 Ma (Naylor, 1971) and a U-Pb zircon upper- intercept age of 364±4 Ma, no. 48 (Aleinikoff and others, 2011). Devonian granitic rocks of southern Vermont. Part of the New Hampshire Plutonic Suite.

Moretown Formation - feldspathic quartzite member (Lower Ordovician to Cambrian?) at surface, covers < 0.1 % of this area

Light-grayish-brown- to tan-weathering biotite-muscovite feldspathic quartzite and muscovitic quartz schist. Part of the metasedimentary host rocks of the North River Igneous Suite. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Biotite-muscovite-plagioclase-quartz schist (Middle to Early Mesoproterozoic) at surface, covers < 0.1 % of this area

A highly heterogeneous unit, distinguished from Y?cms by its generally rusty-weathering, nonlustrous appearance and by the abundance of large albite crystals, conspicuous large plates of muscovite and biotite, and abundant clinozoisite. Locally contains fresh garnet as inclusions in albite, or abundant totally retrograded chlorite-sericite clots after original highly poikiloblastic garnet. Near the contacts with Y1fga, abundant sills of granitic gneiss, plagioclase-tourmaline veins and highly albitic, very coarse grained schist occur. Unit is interbedded near its base with either garnet-muscovite-quartz-plagioclase quartzite (Y2q) or a fine-grained, black hornblende-garnet amphibolite (Y2a) or calc-silicate rock (Y2cs), all of the Mount Holly Complex and containing pegmatite (Y3Cp). Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes. Unit is part of the Problematic rocks at Devils Den in Weston and Danby areas: Near Devils Den and Moses Pond includes albitic biotite-muscovite schist, chloritoid-chlorite-muscovite (±garnet) schist, dolomite marble and minor quartzite which resemble rocks of the Tyson Formation, and retrograde varieties of the paragneisses of the Mount Holly Complex. Because these rocks are structurally compatible with Grenvillian or older folds in the Mount Holly Complex and are transitional into rocks of the Mount Holly Complex, a Mesoproterozoic age is favored. Nevertheless the resemblance to rocks of the Tyson Formation is striking.

Washburn Brook Formation - metamorphosed sedimentary breccia (Upper and Middle Ordovician) at surface, covers < 0.1 % of this area

Metamorphosed sedimentary breccia interlayered with dark-gray slate and micaceous siltstone. Clasts include light-colored, fine-grained metasandstone and metasiltstone of the Albee Formation, dark-gray or greenish-gray slate, and coticule-bearing metasiltstone and chert as well as sparse quartz pebbles. Matrix consists of fine-grained metasandstone, metasiltstone, or dark-gray or greenish-gray slate. Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt.

Ira Formation - limestone (Upper Ordovician) at surface, covers < 0.1 % of this area

Contains basal limestone, locally referred to as the Whipple Marble Member. Unit mapped along east side of the Taconic allochthon south to Bennington. Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

Parker Slate - calcareous sandy conglomerate member (Cambrian) at surface, covers < 0.1 % of this area

Conglomerate with dolostone and sandstone clasts in a calcareous sandy matrix. Cover rocks of the Saint Albans area.

Cavendish Formation - marble member (Early Mesoproterozoic) at surface, covers < 0.1 % of this area

Highly variable unit. Includes white, coarse-grained calcite marble; beige to gray, medium- to coarse-grained phlogopite-tremolite-dolomite-quartz-(±talc) marble; greenish actinolite-dolomite-calcite marble; phlogopite-diopside-scapolite-calcite-dolomite marble; and minor quartzite, diopside quartzite, and schistose bluish-gray marble. Contains pods, stringers, and larger masses of granite pegmatite and interlayered aplitic gneiss. Marble and calc-silicate rocks are identical to units (Y2cs) within the biotite-quartz-plagioclase paragneiss member (Y1,2bg) of the Mount Holly Complex of the Green Mountain massif and eastern domes. Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes. The term “Cavendish Formation” is restricted to two belts of rocks within the Chester dome; the larger belt occurs at Cavendish and on Hawks Mountain, and a less extensive belt, containing similar rocks, occurs near Star Hill. An Early Mesoproterozoic age is here favored for the Cavendish Formation on the basis of (1) the presence of deformed pegmatite (Y3Cp) and areas of Felchville Gneiss (Y1fg and Y1fga) within the Cavendish and (2) the marked resemblance of members of the Cavendish to aluminous and feldspathic schists, calc-silicate rocks, and quartzites within the Mount Holly Complex. Similarities to rocks of the Hoosac Formation are also striking and cannot be altogether dismissed; however, the Hoosac Formation lacks pegmatite and contains distinctive and well-bedded albitic granofels, mafic volcanics, and coarse pebble-to-cobble conglomerate, all absent from the Cavendish. Zircons from a quartzite lens in dolomite marble at locality 4 have Pb-Pb ages between 1,290 and 934 Ma and suggest some of the marble of the Cavendish may be younger than the Felchville Gneiss (Karabinos and others, 1999). Retrograded muscovite-rich, chlorite-spotted, chloritoid-bearing quartz phyllites and garnet granofels and other rocks of the Wilcox Formation (Y2wxs) closely resemble those of the Cavendish Formation, as do chloritic-muscovitic retrograded Y2rs members of the Mount Holly Complex in the Green Mountain massif. Dolomite marble, talc-tremolite rock, diopside quartzite, calc-silicate gneiss, and lustrous chlorite-spotted, chlorite-muscovite-rich retrograded garnet gneiss and schist in the Mount Holly Complex contain abundant pegmatite (Y3Cp) on Blue Ridge Mountain in Chittenden and are identical but lower-grade correlatives of the Cavendish Formation. The coarse garnet-staurolite- and kyanite-bearing Gassetts Schist Member is interpreted to be an Acadian remetamorphosed product of the retrograde aluminous rocks now seen throughout the Mount Holly Complex of the Green Mountain massif and in the Pine Hill area.

Quartz schist and gneiss - quartz-biotite gneiss and quartzite (Middle Mesoproterozoic) at surface, covers < 0.1 % of this area

Unit Y2rs locally includes steel-gray-weathering, garnet (small)-quartz-biotite gneiss and quartzite (Y2bgt). Part of the aluminous schists and gneisses of the Washington Gneiss and Wilcox Formation and related rocks. Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Moosalamoo Formation - feldspathic quartzite and granofels member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Gray to dark-gray, biotite-albite-quartz granofels and flaser-bedded tan to gray feldspathic quartzite; the latter resembles similar rocks of the Dalton Formation (CZdfq), whereas the former resembles albitic rocks of the Hoosac Formation (CZhab). Cover rocks of the Lincoln Mountain massif and northwestern flank of the Green Mountain massif.

Microcline augen gneiss of Lincoln Mountain massif (Late Mesoproterozoic) at surface, covers < 0.1 % of this area

Light- to medium-gray, medium-grained, biotite-quartz-plagioclase-microcline gneiss; contains microcline augen as much as 4 cm in length. Chittenden Intrusive Suite (1,149±8 Ma to 1,119±3 Ma). Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Biotite-quartz diorite gneiss of Vernon dome (Late Ordovician) at surface, covers < 0.1 % of this area

Light-gray, well-foliated subporphyritic biotite (±hornblende)-quartz diorite and trondhjemite gneiss; forms sills in overlying Ammonoosuc Volcanics. Part of the Bronson Hill arch intrusive rocks.

Jay Peak Formation - greenstone member (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Green, carbonate-albite-epidote-chlorite greenstone. Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks.

Equigranular granitic gneiss (Late Mesoproterozoic) at surface, covers < 0.1 % of this area

Equigranular granitic gneiss. Enclaves of metasedimentary units in these granites and associated gneisses are locally albitized and enriched in magnetite; enclaves of highly aluminous altered rocks now contain restites of chloritoid and abundant sericite. U-Pb zircon ages of 1,119±3.3 Ma (no. 15) and 1,121±1.4 Ma (no. 14) determined on samples near Sherburne Center and on Telegraph Hill east of Chittenden Reservoir by Karabinos and Aleinikoff (1990). Chittenden Intrusive Suite (1,149±8 Ma to 1,119±3 Ma). Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Granite and trondhjemite dikes of Chester and Athens domes and west of the Connecticut Valley trough (Devonian) at surface, covers < 0.1 % of this area

Light-gray to white, garnet-muscovite-biotite granodiorite at Gassetts quarry, having a U-Pb zircon SHRIMP age of 392±6 Ma, no. 46 (Aleinikoff and others, 2011), from rims on Proterozoic-age cores (J.N. Aleinikoff, USGS, written commun., 2002); and whitish-gray muscovite-rich quartz monzonite and granodiorite, granite pegmatite, and aplite which occur as crosscutting nonfoliated dikes within the core of the domes and as folded and well-foliated dikes on the east and west flanks of the domes; also granite dikes and small stocks of very light gray to white, muscovite-rich, locally garnet-bearing, fine- to medium-grained biotite-muscovite quartz monzonite and granodiorite, locally orbicular, that intrude cover rocks east of the Green Mountain massif from Jamaica to Northfield, including the Liberty Hill locality and the granodiorite stock east of Plymouth. The latter contains inherited zircon with rims having an imprecise SHRIMP age of about 380 to 390 Ma (Aleinikoff and others, 2011); a similar dike south of Plymouth has a U-Pb zircon SHRIMP age of 365±5 Ma, no. 49 (Aleinikoff and others, 2011). These closely resemble undated white granodiorites of the Bethel area and dikes in the Chester and Athens domes; also resemble small dikes of granite, trondhjemite, and quartz monzonite largely west of the Connecti-cut Valley trough. Devonian granitic rocks of southern Vermont. Part of the New Hampshire Plutonic Suite.

Somerset Reservoir Granite - aplitic to pegmatitic granite (Neoproterozoic) at surface, covers < 0.1 % of this area

White to pinkish-gray, medium-grained plagioclase-microcline-perthite aplitic to pegmatitic granite forms dikes in country rocks and irregular border facies. U-Pb zircon upper-intercept age of 965±4 Ma, no. 19 (Karabinos and Aleinikoff, 1990). Cardinal Brook Intrusive Suite (965±4 Ma to 945±7 Ma). Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Skeels Corners Slate - limestone matrix conglomerate member (Lower Ordovician and Cambrian) at surface, covers < 0.1 % of this area

Limestone and sandstone clasts in a limestone matrix, interbedded with sandstone. Cover rocks of the Saint Albans area.

Ottauquechee Formation - black quartzite member (Cambrian) at surface, covers < 0.1 % of this area

Dark-bluish-gray to black, fine-grained vitreous quartzite. Beds are as thick as 30 m or are thin and interbedded with black phyllite. Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks.

Indian River Slate (Upper Ordovician) at surface, covers < 0.1 % of this area

Deep-maroon and bluish-green-weathering, well-bedded and variegated slate; contains minor centimeter-thick, white-weathering, red and bluish-black cherty layers characteristic of the Mount Merino Formation. Contains graptolites of the C. bicornis Biozone (Berry, 1961). Rocks of the Giddings Brook, Sunset Lake, and Bird Mountain slices. Part of the Taconic Allochthon.

Cram Hill Formation - felsic volcanic member (Middle? and Early Ordovician) at surface, covers < 0.1 % of this area

Light-gray to whitish-gray, fine-grained sericite-quartz-phenocrystic phyllitic metatuff and whitish pyritiferous soda-rhyolite metatuff. Abundant screens and layers occur within mafic rocks of the North River Igneous Suite and at scattered localities north of the Braintree intrusive complex and in the Coburn Hill area. Part of the metasedimentary host rocks of the North River Igneous Suite. Cram Hill Formation: western part of the Cram Hill Formation is in part correlative with Whetstone Hill Member of the Moretown Formation. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

West Halifax Trondhjemite (Ordovician and Late Cambrian) at surface, covers < 0.1 % of this area

Cream-colored, light-gray- to whitish-gray-weathering, coarse-grained chlorite-biotite-muscovite-quartz-plagioclase (±garnet ±hornblende) metatrondhjemite and metatonalite; southern lens near Massachusetts State line is coextensive with trondhjemite in the Hawley Formation. North River Igneous Suite (502±4 Ma to 471.4±3.7 Ma): collection of metatonalite, metatrondhjemite, and metabasalt occurring as intrusive dikes, sills, and small stocks, and possibly meta-andesite and metadacitic tuffs. Correlative with extrusive dacitic metavolcanic and meta-andesitic rocks of the Moretown and Cram Hill Formations. Coextensive in part with igneous rocks of the Hawley Formation of Massachusetts. Part of the Volcanic-arc intrusive and volcanic rocks of the North River Igneous Suite of the Rowe-Hawley zone. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Ascutney Mountain stock – hornfels (Early Cretaceous) at surface, covers < 0.1 % of this area

Dense, compact hornfels consisting of recognizable but altered schists of the country rock. Shown only around main Ascutney Mountain stock in structural continuity with rocks outside the contact aureole. Locally aluminous rocks of the Waits River Formation contain andalusite, sillimanite, cordierite, pleonaste, and corundum; calcareous pelites contain diopside, quartz-wollastonite, plagioclase, grossular garnet, and scapolite. Part of the White Mountain Igneous Suite; Ascutney Mountain stock; Ascutney Mountain igneous complex - Consists of two plutons, a partial ring dike, and screens of volcanic rocks. K-Ar ages of 122 to 120 Ma (Foland and Faul, 1977).

Gile Mountain Formation - amphibolite member (Lower Devonian) at surface, covers < 0.1 % of this area

Hornblende amphibolite and hornblende-plagioclase-quartz granofels; interpreted as metabasaltic and volcaniclastic rocks. Part of the Connecticut Valley Trough.

Hatch Hill Formation (Upper Cambrian) at surface, covers < 0.1 % of this area

Dark-gray to black, sooty- to rusty-weathering, splintery-fractured pyritic slate and phyllite and interbedded bluish-gray dolomitic quartzite. Rocks of the Giddings Brook, Sunset Lake, and Bird Mountain slices. Part of the Taconic Allochthon.

Highgate Formation (Lower Ordovician) at surface, covers < 0.1 % of this area

Banded limestone and calcareous slate with local lenses of conglomerate composed of limestone, sandstone, and dolostone clasts in a sandy limestone matrix. Cover rocks of the Saint Albans area.

Tyson Formation - albitic magnetite granofels member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Gray and greenish-gray, magnetite-chlorite-(biotite)-muscovite-albite-quartz granofels and schist. Similar to gray or green albitic granofels of the Hoosac Formation (CZhab and CZhgab). Eastern and western flank of the Green Mountain massif.

Biotite tonalite gneiss (Middle Mesoproterozoic) at surface, covers < 0.1 % of this area

Predominantly chalky-white-weathering, massive biotite tonalite gneiss. Passes laterally into white, fine-grained trondhjemitic aplite near contacts with larger screens of paragneiss. U-Pb zircon Thermal Ionization Mass Spectrometry (TIMS) age of 1329±37 Ma (McLelland and Chiarenzelli, 1990) obtained from exposure 1.5 km west of Austin Hill on the west side of South Bay, west of Whitehall, N.Y. Contains lenses and screens of rusty sulfidic garnet-biotite-feldspar-quartz schist, dark-gray garnet-feldspar quartzite, and calc-silicate gneiss on south end of Austin Hill. Unit interpreted as intrusive into some paragneiss units that are here older than 1328±32 Ma (McLelland and Chiarenzelli, 1990). Rocks of the Adirondacks in Vermont and in the Whitehall, N.Y., area.

Pinney Hollow Formation - feldspathic quartz schist member (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Light-gray to grayish-green, laminated, gritty feldspathic chlorite-muscovite-plagioclase-quartz schist. Cover rocks of Green Mountain anticlinorium.

Clough Quartzite - quartzite and quartz-cobble metaconglomerate (Lower Silurian) at surface, covers < 0.1 % of this area

Quartzite and quartz-cobble metaconglomerate. Locally contains quartz-cobble conglomerate with abundant dark-gray phyllite matrix that resembles phyllite of the Littleton Formation. Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt.

Pinnacle Formation - cobble and boulder conglomerate member (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Poorly sorted, matrix-supported quartz- and gneiss-cobble to boulder conglomerate, locally containing quartzite boulders as large as 3 m in diameter, in a matrix of gray-weathering magnetite-calcite-chlorite-muscovite-biotite-feldspar schist. Cover rocks of the Lincoln Mountain massif and northwestern flank of the Green Mountain massif.

Ruger Hill facies in the Spring Hill syncline (Ordovician and Late Cambrian) at surface, covers < 0.1 % of this area

Heterogeneous composite intrusive well-layered unit consisting of biotite and hornblende metatrondhjemite, garnet-hornblende-plagioclase amphibolite, and metadiabase dikes; locally called Ruger Hill facies (Onr) in the Spring Hill syncline (Ratcliffe and Armstrong, 2001). Layering thickness ranges from 5 cm to 1 m. Unit may be in part metavolcanic as well as intrusive. Resembles well-layered undated felsic and mafic volcanics intercalated with metasediments of the Cram Hill Formation (Ochv). North River Igneous Suite (502±4 Ma to 471.4±3.7 Ma): collection of metatonalite, metatrondhjemite, and metabasalt occurring as intrusive dikes, sills, and small stocks, and possibly meta-andesite and metadacitic tuffs. Correlative with extrusive dacitic metavolcanic and meta-andesitic rocks of the Moretown and Cram Hill Formations. Coextensive in part with igneous rocks of the Hawley Formation of Massachusetts. Part of the Volcanic-arc intrusive and volcanic rocks of the North River Igneous Suite of the Rowe-Hawley zone. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Cram Hill Formation - carbonaceous schist member (Middle? and Early Ordovician) at surface, covers < 0.1 % of this area

Light-grayish-brown- to tan-weathering, medium-dark-gray, fine-grained garnet (small)-biotite-muscovite phyllite and schist. Similar to phyllite facies (Omwh) in the Whetstone Hill Member of the Moretown Formation. Part of the metasedimentary host rocks of the North River Igneous Suite. Cram Hill Formation: western part of the Cram Hill Formation is in part correlative with Whetstone Hill Member of the Moretown Formation. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Joslin Turn Tonalite (Early Silurian to Middle Ordovician) at surface, covers < 0.1 % of this area

Greenish-gray to light-brownish-gray, medium-grained, weakly foliated metamorphosed tonalite. Primary minerals include quartz, plagioclase, biotite, magnetite, pyrite, and apatite; secondary minerals include chlorite, epidote, sericite, and calcite. Granophyric intergrowths of quartz and plagioclase. U-Pb zircon age of 469±1.5 Ma, no. 27 (Moench and Aleinikoff, 2003). Part of the Highlandcroft Plutonic Suite: Epizonal to mesozonal, foliated and metamorphosed (greenschist facies) plutons exposed northwest of the Ammonoosuc fault. Compositions range from granite to diorite to lesser amounts of gabbro. Part of the Bronson Hill arch intrusive rocks.

Clough Quartzite - lower conglomerate and granofels (Lower Silurian) at surface, covers < 0.1 % of this area

On Skitchewaug Mountain, lower conglomerate and granofels. Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt.

Carbonaceous sulfidic schist (Middle Mesoproterozoic) at surface, covers < 0.1 % of this area

Dark-gray, rusty-weathering carbonaceous to graphitic schist associated with quartzite and calc-silicate rock near Killington. Part of the aluminous schists and gneisses of the Washington Gneiss and Wilcox Formation and related rocks. Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Pinnacle Formation - metabasalt and volcaniclastic rocks, undifferentiated (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Largely carbonate-epidote-albite-chlorite (±actinolite) greenstones. Cover rocks of the Lincoln Mountain massif and northwestern flank of the Green Mountain massif.

Pinnacle Formation - light-gray phyllitic conglomerate member (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Feldspathic biotite phyllitic metawacke interlayered with lenses of quartz, feldspar, and gneiss-pebble to -cobble conglomerate. Cover rocks of the Lincoln Mountain massif and northwestern flank of the Green Mountain massif.

Belvidere Mountain Structural Complex - ultramafic rocks (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Brown to white-weathering, green, massive, moderately to fully serpentinized dunite and peridotite and schistose serpentinite; rusty-weathering, medium-grained talc-carbonate rock and quartz-carbonate (magnesite) rock. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Moretown Formation - Whetstone Hill Member - metasiltstone facies (Lower Ordovician to Cambrian?) at surface, covers < 0.1 % of this area

Pale-greenish-gray, finely laminated, magnetite-chlorite-biotite feldspathic metasiltstone and pale-greenish-yellow-weathering muscovite-chlorite-quartz phyllite. Part of the metasedimentary host rocks of the North River Igneous Suite. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Aplitic gneiss (Middle Mesoproterozoic) at surface, covers < 0.1 % of this area

Light-gray to white, fine-grained aplitic granite gneiss as border of Y2gg or as thin dikes or sills in paragneiss units. Stratton Mountain Intrusive Suite (Middle Mesoproterozoic) (1,244±8 Ma to 1,221±4 Ma). Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Hortonville Formation - limestone (Upper Ordovician) at surface, covers < 0.1 % of this area

Near base contains bluish-gray, granular, smooth-weathering fossiliferous limestone. Unit mapped west of the Taconic allochthon, and northwest of the Sudbury slice. Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

Plymouth Formation - dolostone member (Cambrian) at surface, covers < 0.1 % of this area

Light-gray- to beige-weathering massive dolostone and bluish-gray-weathering mottled dolostone breccia and conglomerate, passing upward into more thinly bedded bluish-gray and buff dolostone breccia; dark-gray phyllitic dolostone and limestone in upper part. Correlative in part with boulder and conglomerate beds of the Dunham Dolostone near Rutland and with similar beds in the upper part of the Forestdale Formation. Eastern flank of the Green Mountain massif and eastern domes.

Cram Hill Formation - ironstone, quartzite, and coticule member (Middle? and Early Ordovician) at surface, covers < 0.1 % of this area

Dark-gray- to sooty-black-weathering siliceous ironstone, magnetite quartzite, garnet quartzite, rusty-weathering amphibolite, coticule, and pods of orangey-gray to pinkish-gray-weathering dolostone. Part of the metasedimentary host rocks of the North River Igneous Suite. Cram Hill Formation: western part of the Cram Hill Formation is in part correlative with Whetstone Hill Member of the Moretown Formation. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Comerford Intrusive Complex - pegmatitic metatonalite to metagabbro (Late Silurian) at surface, covers < 0.1 % of this area

Nonfoliated to foliated pegmatitic metatonalite to metagabbro. Part of the Lake Memphremagog Intrusive Suite (425±3 Ma to 418.5±2 Ma).

Potsdam Sandstone (Upper Cambrian) at surface, covers < 0.1 % of this area

Light-gray, tan, and dark-gray, well- bedded pebbly quartzite, crossbedded vitreous quartzite, and local conglomerate. Part of the Beekmantown Group. Rocks of the Laurentian Margin. Part of the Adirondack lowlands and Lake Champlain lowlands (west of the Orwell and Champlain thrusts).

Derby pluton - granodiorite (Devonian) at surface, covers < 0.1 % of this area

Rim zone of granodiorite of unit Ddbg. Rb/Sr whole-rock isochron age of 370±17 Ma (Ayuso and Arth, 1992). Igneous rocks of the Northeast Kingdom batholith of Ayuso and Arth (1992). Part of the New Hampshire Plutonic Suite.

Littleton Formation - metarhyolite (Lower Devonian) at surface, covers < 0.1 % of this area

White-weathering, medium- to dark-gray, foliated and laminated, aphanitic to very fine grained granofels to schist or metatuff, welded tuff, and lithic tuff commonly with a few percent millimeter-size quartz and microcline phenocrysts. U-Pb zircon age of 407.5±3.9 Ma, no. 44 (Rankin and Tucker, 2000). Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt.

Hoosac Formation - quartzite member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Light-gray-, yellowish-gray- to dark-dull-gray-weathering, biotite or muscovite quartzite, feldspathic quartzite, and pebbly muscovitic quartzite, commonly occuring as basal member or as layers in schist member (CZhs). Eastern flank of the Green Mountain massif and eastern domes.

Ascutney Mountain stock – granite (Early Cretaceous) at surface, covers < 0.1 % of this area

Medium- to coarse-grained biotite-microperthite-orthoclase-albite granite. Part of the White Mountain Igneous Suite; Ascutney Mountain igneous complex - Consists of two plutons, a partial ring dike, and screens of volcanic rocks. K-Ar ages of 122 to 120 Ma (Foland and Faul, 1977).

Calcite marble (Middle Mesoproterozoic) at surface, covers < 0.1 % of this area

Light-bluish-gray and white, coarse- and medium-grained calcite-diopside marble and calcite-diopside-talc marble in beds or pods less than 5 m thick, interbedded with or passing laterally into other calc-silicate rock. Part of the aluminous schists and gneisses of the Washington Gneiss and Wilcox Formation and related rocks. Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Whipstock Breccia in the Walloomsac Formation (Upper Ordovician) at surface, covers < 0.1 % of this area

Largely a tectonic breccia formed in situ; contains abundant pseudo-pebbles. Part of the Taconic Allochthon. Wildflysch-like conglomerates within the Hortonville, Ira, and Walloomsac Formations occur as local areas of black slate rich in inclusions of quartzite, greenish-gray slate, wacke, and punky-weathering bluish-gray limestone, interpreted as sedimentary breccias, deposited in front of the advancing Taconic allochthon (Upper Ordovician) (Zen, 1961; Potter, 1972; Fisher, 1985). Exposed near the western and northern margin of the allochthon and in the Bennington area at the type Whipstock. Here and at many localities the Forbes Hill and Whipstock breccias are tectonic breccias formed in situ by disruption of thin to thick beds, laminae, and carbonate-quartz-sulfide veins rather than clastic sedimentary rocks. The cleavage and related folding commonly is a late strain-slip cleavage characterized by a strong down-plunge lineation parallel to reclined hingelines of minor folds of foliation and compositional layering. Units are retained although interpretation as sedimentary wildflysch deposits is in part questionable.

Dalton Formation - phyllite member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Rusty-tan to gray, thinly layered phyllite, tourmaline-biotite-muscovite-quartz phyllite, and quartzite mapped along western flank of the Green Mountain massif in the South Wallingford area. Unit interfingers to the north with rocks of the Tyson Formation and to the east with rocks of the Hoosac Formation. Cover rocks of the Southern Green Mountains.

Metatrondhjemite and metatonalite (Ordovician and Late Cambrian) at surface, covers < 0.1 % of this area

Light-gray to whitish-gray, coarse-grained muscovite-biotite-quartz-plagioclase metatrondhjemite on the east flank of the Chester dome; similar to Onb, Onnt, and Ontw. North River Igneous Suite (502±4 Ma to 471.4±3.7 Ma): collection of metatonalite, metatrondhjemite, and metabasalt occurring as intrusive dikes, sills, and small stocks, and possibly meta-andesite and metadacitic tuffs. Correlative with extrusive dacitic metavolcanic and meta-andesitic rocks of the Moretown and Cram Hill Formations. Coextensive in part with igneous rocks of the Hawley Formation of Massachusetts. Part of the Volcanic-arc intrusive and volcanic rocks of the North River Igneous Suite of the Rowe-Hawley zone. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Echo Pond pluton - granite (Devonian) at surface, covers < 0.1 % of this area

Inner zone of granite. Igneous rocks of the Northeast Kingdom batholith of Ayuso and Arth (1992). Part of the New Hampshire Plutonic Suite.

Moretown Formation - quartz schist member (Lower Ordovician to Cambrian?) at surface, covers < 0.1 % of this area

Bluish-black, rusty-weathering, fine-grained albite-sericite-chlorite-quartz schist with pyrite. Part of the metasedimentary host rocks of the North River Igneous Suite. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Pinnacle Formation - quartzite and quartz-pebble conglomerate member (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Light-gray quartz-feldspar conglomerate and quartzite. Cover rocks of the Lincoln Mountain massif and northwestern flank of the Green Mountain massif.

West Charleston pluton (Devonian) at surface, covers < 0.1 % of this area

Dark-gray, medium- to coarse-grained, massive, quartz-biotite-hornblende (±pyroxene) gabbro and diorite. Igneous rocks of the Northeast Kingdom batholith of Ayuso and Arth (1992). Part of the New Hampshire Plutonic Suite.

Hybrid rock: mangeritic to charnockitic gneiss (Middle Proterozoic) at surface, covers < 0.1 % of this area

With xenocrysts of calcic andesine and, locally, xenoliths of anorthosite; with increasing percentage of anorthosite component, passes gradationally into anorthositic rocks.

Mylonitic gneiss (Age uncertain) at surface, covers < 0.1 % of this area

Highly schistose, biotite-muscovite (±chlorite) feldspathic mylonite and mylonitic gneiss mapped near Brandon Gap; in the Pine Hill slice near South Wallingford is mapped as Yur. Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Hathaway Formation (Upper Ordovician) at surface, covers < 0.1 % of this area

Clasts of limestone, dolostone, sandstone, and chert within beds of black shale and chert. Rocks of the Laurentian Margin. Part of the Adirondack lowlands and Lake Champlain lowlands (west of the Orwell and Champlain thrusts).

Albee Formation - magnetite-rich areas (Ordovician and Cambrian) at surface, covers < 0.1 % of this area

Magnetite-rich areas of the Albee Formation (OCal) - Shown as an overprint. Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt.

Waits River Formation - quartz-cobble and schistose metaconglomerate member (Lower Devonian and Upper Silurian) at surface, covers < 0.1 % of this area

Light-gray muscovite-quartz schist and quartz conglomerate and dark-gray carbonaceous, polymict schistose quartz conglomerate, associated with DSwb, DSwb/Dl, DSws, and DSwv southeast of Springfield. Part of the Connecticut Valley Trough.

Rowe Schist - garnet-biotite feldspathic schist member (Cambrian and Neoproterozoic?) at surface, covers < 0.1 % of this area

Dark-grayish-brown-weathering, coarse-grained garnet-biotite-plagioclase-quartz schist. Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks. Rowe Schist: Mapped in southern Vermont where the uppermost part is continuous with amphibolites, schists, and feldspathic schists of the Rowe Schist of Massachusetts. These upper units are continuous with rocks of the Stowe Formation to the north. Units in the middle and lowermost structural positions (above the Hoosac Formation) are in a similar structural position as rocks of the Ottauquechee and Pinney Hollow Formations, although structural continuity and correlations with the Ottauquechee and Pinney Hollow Formations are uncertain owing to extensive structural duplication by thrust faulting and folding.

Pinney Hollow Formation - chloritoid-rich (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Chloritoid-rich rocks appear gritty owing to distributed porphyroblasts of chloritoid. Unit is locally albitic and contains minor beds of quartzite. Cover rocks of Green Mountain anticlinorium.

Braintree Intrusive Complex - biotite-bearing metagranodiorite, metagranite, and meta-aplite of the Mount Nevis pluton (Late Silurian) at surface, covers < 0.1 % of this area

Yellowish-gray to light-gray, medium- to coarse-grained magnetite-biotite-mesoperthite granodiorite and granite having a U-Pb zircon SHRIMP age of 421±7 Ma, no. 38 (Aleinikoff and others, 2011). Has mutually intrusive contacts with associated metadiorites. Unmapped dike of Sbg in the layered, mixed felsic and mafic rocks (Onbm) of the North River Igneous Suite at Bridgewater has a U-Pb zircon age of 418±1 Ma, no. 37 (Aleinikoff and Karabinos, 1990). Part of the Lake Memphremagog Intrusive Suite (425±3 Ma to 418.5±2 Ma).

Braintree Intrusive Complex - metadiorite to metamonzodiorite (Late Silurian) at surface, covers < 0.1 % of this area

Medium-gray-weathering, porphyritic dikes and sills of fine- to medium-grained hornblende-biotite diorite and quartz diorite, and coarse-grained quartz monzodiorite. Has a U-Pb zircon TIMs age of 419±0.39 Ma, no. 36 (Black and others, 2004). Narrow zone of garnet-biotite-plagioclase-cordierite hornfels in the Moretown Formation postdates dominant foliation (Taconian) in host rocks. Part of the Lake Memphremagog Intrusive Suite (425±3 Ma to 418.5±2 Ma).

Dolomite marble (Middle Mesoproterozoic) at surface, covers < 0.1 % of this area

Light-gray to yellowish-gray, coarse-grained dolomite-phlogopite-scapolite marble; pyritiferous varieties weather salmon pink to beige. Unit occurs on West Mountain in Chittenden, in Sherburne Center, Weston, and in the Pine Hill slice; is commonly associated with tremolite-talc marble and tremolite-talc schist. Part of the aluminous schists and gneisses of the Washington Gneiss and Wilcox Formation and related rocks. Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Plagioclase-phenocrystic tonalite gneiss (Early Mesoproterozoic?) at surface, covers < 0.1 % of this area

Coarse-grained facies of the Baileys Mills tonalitic gneiss exposed on the northeast flank of the Chester dome. South Londonderry Igneous Suite (Middle and Early Mesoproterozoic) (1,393±9 Ma to 1,309±6 Ma). Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Hornblende gabbro-diorite (Mesoproterozoic) at surface, covers < 0.1 % of this area

Biotite-hornblende (±pyroxene) gabbro and diorite at Robinson Hill in Shrewsbury; exhibits fine-grained chill contact that crosscuts paragneiss units. Unit also in Lincoln Mountain massif and at Brandon Gap; similar rock mapped in the Adirondacks. Chittenden Intrusive Suite (1,149±8 Ma to 1,119±3 Ma). Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Clarendon Springs Formation - clacite marble (Upper Cambrian) at surface, covers < 0.1 % of this area

Locally contains light-bluish-gray to whitish-gray calcite marble within dolostone and beneath the calcitic marbles of the overlying Shelburne Marble. Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

Moretown Formation - Whetstone Hill Member - coticule and quartzite facies (Lower Ordovician to Cambrian?) at surface, covers < 0.1 % of this area

Dark-gray to light-gray, vitreous magnetite quartzite, and coticule. Part of the metasedimentary host rocks of the North River Igneous Suite. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Netop Formation - albite-metasiltstone (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Greenish-gray laminated albite-metasiltstone. The Netop Formation may be in part equivalent in age and facies to parts of the West Castleton and Hatch Hill Formations, but may extend lower and into the Neoproterozoic. Rocks of the Dorset Mountain slice (includes Dorset Mountain proper and Mount Equinox, southward to West Mountain near Bennington). Part of the Taconic Allochthon.

Muscovite-chlorite-garnet schist (Middle to Early Mesoproterozoic) at surface, covers < 0.1 % of this area

Light-silvery-green to grayish-green, lustrous muscovite-chlorite-quartz (±garnet±chloritoid±ilmenite) schist and biotite-albite-muscovite-quartz schist. Unit is highly variable both in texture and in composition (from ultrafine-grained phyllonitic schist to medium-grained muscovite-garnet schist). Albitic varieties tend to contain more biotite and less muscovite. Rock is highly retrograded and contains abundant chlorite derived from the breakdown of garnet that contained large anhedral quartz and grains of coarse muscovite and biotite. Robust grains of rutile are abundant. Chloritoid commonly occurs in the fine-grained sericitic matrix but locally is found within large subhedral garnets. The contact with adjacent Y?mfs is gradational and determined by a higher abundance of biotite (commonly chloritized) and albite in Y?mfs near Y?cms. The contact with Y2rs of the Mount Holly Complex is gradational. Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes. Unit is part of the Problematic rocks at Devils Den in Weston and Danby areas: Near Devils Den and Moses Pond includes albitic biotite-muscovite schist, chloritoid-chlorite-muscovite (±garnet) schist, dolomite marble and minor quartzite which resemble rocks of the Tyson Formation, and retrograde varieties of the paragneisses of the Mount Holly Complex. Because these rocks are structurally compatible with Grenvillian or older folds in the Mount Holly Complex and are transitional into rocks of the Mount Holly Complex, a Mesoproterozoic age is favored. Nevertheless the resemblance to rocks of the Tyson Formation is striking.

Moretown Formation - hornblende-spotted “dioritic” amphibolite (Lower Ordovician to Cambrian?) at surface, covers < 0.1 % of this area

Hornblende-spotted “dioritic” amphibolite. Part of the metasedimentary host rocks of the North River Igneous Suite. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Fitch Formation (Lower Devonian and Upper Silurian) at surface, covers < 0.1 % of this area

Metamorphosed limestone, calcareous sandstone, siltstone, and pelite. Some limestone conglomerate and polymict conglomerate with calcareous matrix. Locally equivalent to Madrid and Smalls Falls Formations in Chesterfield, N.H., area. Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt.

Potsdam Sandstone (Cambrian) at surface, covers < 0.1 % of this area

Potsdam Sandstone (Covey Hill in Quebec)

Tonalite gneiss (Ordovician and Late Cambrian) at surface, covers < 0.1 % of this area

Medium-grayish-green, medium-grained hornblende-biotite tonalite gneiss, with minor amphibolite. U-Pb zircon TIMS age of 486±3 Ma, no. 24 (Aleinikoff and others, 2011), from 4 km northwest of Brockways Mills, near Bartonsville. North River Igneous Suite (502±4 Ma to 471.4±3.7 Ma): collection of metatonalite, metatrondhjemite, and metabasalt occurring as intrusive dikes, sills, and small stocks, and possibly meta-andesite and metadacitic tuffs. Correlative with extrusive dacitic metavolcanic and meta-andesitic rocks of the Moretown and Cram Hill Formations. Coextensive in part with igneous rocks of the Hawley Formation of Massachusetts. Part of the Volcanic-arc intrusive and volcanic rocks of the North River Igneous Suite of the Rowe-Hawley zone. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Biotite pegmatoid granitic gneiss (Late Mesoproterozoic) at surface, covers < 0.1 % of this area

Extensive areas of biotite pegmatoid granitic gneiss, locally muscovite-bearing. Enclaves of metasedimentary units in these granites and associated gneisses are locally albitized and enriched in magnetite; enclaves of highly aluminous altered rocks now contain restites of chloritoid and abundant sericite. U-Pb zircon ages of 1,119±3.3 Ma (no. 15) and 1,121±1.4 Ma (no. 14) determined on samples near Sherburne Center and on Telegraph Hill east of Chittenden Reservoir by Karabinos and Aleinikoff (1990). Chittenden Intrusive Suite (1,149±8 Ma to 1,119±3 Ma). Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Biotite-epidote-quartz gneiss and epidotic quartzite (Middle and Early Mesoproterozoic) at surface, covers < 0.1 % of this area

Light-pale-yellowish-green to gray quartzite gneiss containing abundant epidote and locally magnetite, and frosted round grains of quartz associated with diopside-bearing quartzite. Part of the aluminous schists and gneisses of the Washington Gneiss and Wilcox Formation and related rocks. Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Hoosac Formation - dolomite marble member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Light-gray-, cream- or pinkish-gray-weathering, medium- to fine-grained phlogopite-quartz-dolomite marble. Occurs as thin beds in gray albitic granofels member (CZhab); locally contains beds of vitreous to bluish-gray laminated quartzite. Eastern flank of the Green Mountain massif and eastern domes.

Walloomsac Formation - limestone (Upper Ordovician) at surface, covers < 0.1 % of this area

Basal limestone member. Tectonically shredded, silty varieties near and on Whipstock Hill constitute the Whipstock Breccia Member of Potter (1972) (Oww). Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

Cuttingsville stock – syenite (Early Cretaceous) at surface, covers < 0.1 % of this area

Nepheline and sodalite syenite, hornblende syenite. Part of the White Mountain Igneous Suite; Cuttingsville stock - Composite stock and intrusive breccia dikes consisting of augite and hastingsite syenite, nepheline and sodalite syenite, essexite, and monzodiorite. Associated dikes of monchiquite, camptonite, boston-ite, and spessartite. Average of five K-Ar ages 101 Ma; ages range between 103±4 and 99±2 Ma (Armstrong and Stump, 1971).

Willoughby pluton - inner zone (Devonian) at surface, covers < 0.1 % of this area

Light-gray to pink, medium- to very coarse grained, massive, miarolitic garnet-muscovite peraluminous leucogranite. Inner hydrothermally altered zone. Rb/Sr whole-rock age of 376±9 Ma (Ayuso and Arth, 1992). Igneous rocks of the Northeast Kingdom batholith of Ayuso and Arth (1992). Part of the New Hampshire Plutonic Suite.

Hoosac Formation (Lower Cambrian and Proterozoic Z) at surface, covers < 0.1 % of this area

Undifferentiated Hoosac Formation.

Moosalamoo Formation - magnetite metasiltstone member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Grayish-brown- to pale-green-weathering, well-laminated, magnetite-studded chloritic metasiltstone; near base contains magnetite-cemented quartz-pebble conglomerate and bedded magnetite quartzite. Directly overlies dolostones of the Forestdale Formation. Cover rocks of the Lincoln Mountain massif and northwestern flank of the Green Mountain massif.

Albite-magnetite-studded gneiss (Late Mesoproterozoic) at surface, covers < 0.1 % of this area

Gray or greenish-gray, albite- and magnetite-studded granulose biotite-quartz-plagioclase gneiss, containing chloritized biotite and garnet. Occurs as altered varieties of Y1,2bg near 1,150-Ma intrusive augen gneisses of the Chittenden Intrusive Suite (Y3Ama); in the Lincoln Mountain massif a dark-gray biotite-microcline-chlorite-spotted gneiss contains magnetite grains as much as 1 cm in diameter. Part of the altered rocks adjacent to the Chittenden Intrusive Suite. Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Fayston Formation - carbonaceous albite schist member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Gray to medium-dark-gray, rusty-weathering, carbonaceous albite-chlorite-quartz-muscovite schist, containing porphyroblasts of black albite. Unit resembles gray albitic granofels and schist of the Hoosac Formation (CZhab). Cover rocks north of the Lincoln Mountain massif.

Shaw Mountain Formation - basal volcaniclastic and metasedimentary member (Upper to Lower Silurian) at surface, covers < 0.1 % of this area

Heterogeneous, thin (<10 m thick) unit of interbedded quartzite, amphibolite, felsic granofels, and phyllite, occurring at the base of the Waits River Formation on the north end of the Chester dome. Interpreted as recycled volcaniclastic rocks derived from the underlying volcanic and intrusive rocks in the Cram Hill Formation. Part of the Connecticut Valley Trough.

Pinney Hollow Formation - metawacke member (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Silvery-gray, “pinstriped,” coarse- to medium-grained, blue-quartz-pebble chlorite-biotite-plagioclase-quartz metawacke; locally conglomeratic and rich in epidote. Cover rocks of Green Mountain anticlinorium.

Garnet-biotite gneiss (Middle Mesoproterozoic) at surface, covers < 0.1 % of this area

Dark-gray- to rusty-grayish-brown-weathering, sulfidic muscovite-biotite-magnetite gneiss or schist marked by abundant small garnets, biotite, and fine laminae of quartz and plagioclase. Contains thin belts of amphibolite and calc-silicate gneiss. Part of the aluminous schists and gneisses of the Washington Gneiss and Wilcox Formation and related rocks. Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Cram Hill Formation - Coburn Hill Metabasalt member (Middle? and Early Ordovician) at surface, covers < 0.1 % of this area

Light-green, fine- to medium-grained, massive carbonate-biotite-quartz-sphene-chlorite-actinolite-epidote greenstone with deformed pillows; interfingers with the Umbrella Hill Conglomerate Member (Ochuc) and with phyllite-chip conglomerate (Ochsb). Part of the Cram Hill Formation of the Newport Center area. Part of the metasedimentary host rocks of the North River Igneous Suite. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Tyson Formation - quartzite member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Gray to very light gray, vitreous and nonvitreous, massive to thin-bedded quartzite, magnetite and biotite quartzite, and feldspathic quartz-ite, locally interbedded with dolostone. Similar to quartzite in the Forestdale Formation (CZfq). Eastern and western flank of the Green Mountain massif.

Quartzite - undifferentiated (Early Mesoproterozoic) at surface, covers < 0.1 % of this area

Tan to rusty-brown or gray, thinly layered garnet-biotite quartzite and schistose quartzite associated with aluminous schists and calc-silicate rocks or interbedded within biotite-quartz-plagioclase paragneiss. Unit probably occurs at various stratigraphic levels; may be Early Mesoproterozoic in part (Y1q). Part of the aluminous schists and gneisses of the Washington Gneiss and Wilcox Formation and related rocks. Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Belvidere Mountain Structural Complex - albite gneiss (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

White, light-gray- and green-banded, fine- to medium-grained, well-layered epidote-white mica-quartz-albite (±garnet±magnetite) gneiss; contains plagioclase and polycrystalline quartz porphyroblasts. The 0.5- to 2-cm-thick layers are defined by variations in the amount of quartz, albite, white mica, and chlorite. Gneiss is similar to gneiss at the base of the Tillotson Peak Structural Complex. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Wilcox Formation - quartzite member (Middle Mesoproterozoic) at surface, covers < 0.1 % of this area

Tan, yellowish-gray-weathering garnet-muscovite quartzite and feldspathic retrograde-garnet quartz gneiss. Part of the aluminous schists and gneisses of the Washington Gneiss and Wilcox Formation and related rocks. Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Talc-carbonate schist (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Cream-colored to light-bluish-gray, brown-weathering, talc-carbonate schist and talc-cabonate-rich rocks. Part of Ultramafic rocks: occur as tectonic slivers and olistoliths in blocks within the Hazens Notch, Ottauquechee, Stowe, Rowe, and Moretown Formations. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Belvidere Mountain Structural Complex - fine-grained amphibolite (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Bluish-gray, fine- to medium-grained albite-horn-blende-epidote-actinolite (±garnet) amphibolite and quartz-bearing amphibolite. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Eagle Bridge Quartzite (Lower Cambrian) at surface, covers < 0.1 % of this area

Dull-gray, pitted, and bluish-gray dolomitic quartz wacke and quartzite distinguished by small pebbles and grains of dark-blue to black quartz, dacitic rock fragments, and abundant plagioclase. Beds resembling the Eagle Bridge Quartzite may occur at several stratigraphic positions within the black slate and gray phyllite of the West Castleton and Hatch Hill(?) Formations, undifferentiated (Cwcu), and near the base of the Poultney Formation, and probably are not all correlative. Rocks of the Giddings Brook, Sunset Lake, and Bird Mountain slices. Part of the Taconic Allochthon.

Forestdale Formation - phyllite and dolostone breccia member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Dark-gray to sooty-black carbonaceous phyllite, interbedded dolostone boulder conglomerate to breccia, and blue- and gray-mottled sulfidic dolostone. Cover rocks of the Lincoln Mountain massif and northwestern flank of the Green Mountain massif.

Bull Formation - Mud Pond Quartzite member (Lower Cambrian) at surface, covers < 0.1 % of this area

Buff- to gray-weathering vitreous quartzite as much as 6 m thick, containing deeply weathered ovoidal areas of carbonate-cemented quartzite. Rocks of the Giddings Brook, Sunset Lake, and Bird Mountain slices. Part of the Taconic Allochthon.

Moretown Formation - quartzite member (Lower Ordovician to Cambrian?) at surface, covers < 0.1 % of this area

Dark-gray to steel-bluish-gray vitreous quartzite in beds as much as 10 m thick but commonly less than 1 m thick. Resembles quartzites of the Ottauquechee Formation (Cobq). Part of the metasedimentary host rocks of the North River Igneous Suite. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Fayston Formation - greenstone member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Dark-green, pitted-weathering, foliated carbonate-albite-chlorite (±magnetite±epidote) greenstone or amphibolite. Cover rocks north of the Lincoln Mountain massif.

Carbonate - limestone (Cambrian and Neoproterozoic?) at surface, covers < 0.1 % of this area

Pods, lenses, or zones of thinly bedded limestone (ls), dolostone (d), and limestone conglomerate in the Mettawee slate facies in the Bull Formation, West Castleton Formation, and Hatch Hill Formation. These rocks locally contain Lower Cambrian fossils, but may range in age from Neoproterozoic to Late Cambrian. Rocks of the Giddings Brook, Sunset Lake, and Bird Mountain slices. Part of the Taconic Allochthon.

Belvidere Mountain Structural Complex - coarse-grained amphibolite (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Dark-gray, coarse-grained amphibolite and layered amphibolite composed of barroisite, epidote, garnet, actinolite, albite, chlorite, sphene, sericite, biotite, and calcite. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Fort Cassin Formation - Sciota Limestone Member (Middle and Lower Ordovician) at surface, covers < 0.1 % of this area

Light-gray, fine- grained, and dark-gray, fossiliferous, and platy bluish-gray limestone. Contains upper Ibexian to lower Whiterockian conodonts at the type locality near Sciota School House, in the Benson quadrangle (J.E. Repetski, USGS, written commun., 2004). Part of the Beekmantown Group. Rocks of the Laurentian Margin. Part of the Adirondack lowlands and Lake Champlain lowlands (west of the Orwell and Champlain thrusts).

Monadnock Mountain pluton - granite (Middle Jurassic) at surface, covers < 0.1 % of this area

Hornblende-biotite-microperthite granite, gradational into quartz syenite. Monadnock Mountain pluton: Composite stock of quartz syenite, syenite granite, and essexite. K-Ar age of 175±4 Ma (Foland and Faul, 1977). Part of the White Mountain Igneous Suite.

Bethlehem Gneiss (Early Devonian) at surface, covers < 0.1 % of this area

Medium- to coarse-grained, equigranular to porphyritic, muscovite-biotite-microcline-plagioclase metaquartz monzonite; contains garnet, sillimanite-andalusite and cordierite; intrudes rocks of the Rangeley Formation in New Hampshire. U-Pb zircon age of 407±5 Ma, no. 43 (Kohn and others, 1992) at Bellows Falls. Part of the Bronson Hill arch intrusive rocks.

Forestdale Formation - quartzite member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Grayish-tan to light-gray vitreous quartzite and white feldspathic gritty quartzite. Cover rocks of the Lincoln Mountain massif and northwestern flank of the Green Mountain massif.

Hoosac Formation - albite granofels and gneiss-boulder conglomerate member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Light-gray, massive, coarse-grained biotite-white albite-quartz granofels like CZhab but containing boulders of pegmatite and of granitic gneiss, and disarticulated beds of albitic granofels as pseudoconglomerate. Eastern flank of the Green Mountain massif and eastern domes.

Hoosac Formation - conglomerate and quartzite member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Light-grayish-tan-weathering, biotite-muscovite-quartz conglomerate and pebbly muscovite quartzite, and dark-medium-gray blue-quartz biotite quartzite and schist. Eastern flank of the Green Mountain massif and eastern domes.

Cuttingsville stock - quartz syenite (Early Cretaceous) at surface, covers < 0.1 % of this area

Quartz syenite. Part of the White Mountain Igneous Suite; Cuttingsville stock - Composite stock and intrusive breccia dikes consisting of augite and hastingsite syenite, nepheline and sodalite syenite, essexite, and monzodiorite. Associated dikes of monchiquite, camptonite, boston-ite, and spessartite. Average of five K-Ar ages 101 Ma; ages range between 103±4 and 99±2 Ma (Armstrong and Stump, 1971).

Fayston Formation - foliated metawacke member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Salt-and-pepper-colored, medium- to coarse-grained quartz-albite-biotite gneiss. Cover rocks north of the Lincoln Mountain massif.

Stamford Granite Gneiss (Proterozoic Y) at surface, covers < 0.1 % of this area

White to gray biotite-oligoclase-microcline Rapakivi granite gneiss containing blue quartz. Intrudes Yb, Ybu.

Sandy phyllite, granofels, and cherty phyllite (Upper Ordovician) at surface, covers < 0.1 % of this area

Gray and grayish-green rocks associated with Whipstock breccia on Whipstock Hill but of uncertain correlation. Part of the Taconic Allochthon.

Proctor Hill granodiorite gneiss - aplitic and hornblende-rich reaction zones (Middle Mesoproterozoic) at surface, covers < 0.1 % of this area

Within unit Y2phg: aplitic and hornblende-rich reaction zones where in contact with calc-silicate rocks. Crosscuts all paragneiss units; is a thoroughly gneissic rock. Correlated with the Ludlow Mountain granodiorite gneiss. South Londonderry Igneous Suite (Middle and Early Mesoproterozoic) (1,393±9 Ma to 1,309±6 Ma). Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Wilcox Formation - calc-silicate gneiss and marble member (Middle Mesoproterozoic) at surface, covers < 0.1 % of this area

Dark-green, massive, diopside-hornblende rock, lenses of bluish-gray to gray, medium- to coarse-grained calcite marble and calcite-diopside marble and dolomitic talc-phlogopite-tremolite schist. Part of the aluminous schists and gneisses of the Washington Gneiss and Wilcox Formation and related rocks. Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

French Pond Granite (Late Devonian) at surface, covers < 0.1 % of this area

Pink to gray, nonfoliated, porphyritic to coarse-grained biotite granite; phenocrysts of potassium feldspar are as large as 2 by 3 cm. U-Pb zircon age of 364±5 Ma, no. 50 (Moench and Aleinikoff, 2003). Part of the Bronson Hill arch intrusive rocks.

Cram Hill Formation - quartzite and quartz-pebble conglomerate member (Middle? and Early Ordovician) at surface, covers < 0.1 % of this area

Tan- to gray-weathering, quartz-pebble and -cobble conglomerate, feldspathic quartzite and associated slabby, rusty-weathering amphibolite and coticule. Part of the metasedimentary host rocks of the North River Igneous Suite. Cram Hill Formation: western part of the Cram Hill Formation is in part correlative with Whetstone Hill Member of the Moretown Formation. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Mount Abraham Formation - with minor porphyroblasts (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Lustrous, silvery-green to bluish-gray, fine- to medium-grained, white mica-chloritoid-quartz-chlorite schist and phyllite, locally with minor garnet and magnetite porphyroblasts (CZap). Distinctive chlorite streaks and 1-cm rusty needles of altered kyanite are common. Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks.

Mount Merino Formation (Upper Ordovician) at surface, covers < 0.1 % of this area

Light-gray, powdery-weathering, and red, green, and dark-gray, thinly bedded siliceous argillite and mudstone distinguished from the Indian River Slate by abundance of cherty siliceous layers. Rocks of the Giddings Brook, Sunset Lake, and Bird Mountain slices. Part of the Taconic Allochthon.

Biotite-quartz-plagioclase gneiss (Middle to Early Mesoproterozoic) at surface, covers < 0.1 % of this area

Light-greenish-gray to pinkish-gray, well-foliated and well-layered quartz-rich gneiss and more mafic biotite-hornblende-pyroxene-quartz-plagioclase gneiss irregularly distributed within unit. Unit may be in part older than the tonalitic gneiss (Y2bt). Paragneiss. Rocks of the Adirondacks in Vermont and in the Whitehall, N.Y., area.

Clough Quartzite - upper quartzite (Lower Silurian) at surface, covers < 0.1 % of this area

On Skitchewaug Mountain, upper quartzite. Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt.

Moretown Formation - felsic metavolcanic member (Lower Ordovician to Cambrian?) at surface, covers < 0.1 % of this area

Gray, purplish-gray, and light-gray dacitic to andesitic metavolcanic and metavolcaniclastic rocks, similar to Omwhv. Part of the metasedimentary host rocks of the North River Igneous Suite. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Fayston Formation - quartzite member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

White quartzite and tan to light-gray, medium-grained muscovite quartzite locally rich in magnetite. Resembles quartzite of the Tyson Formation (CZtq). Cover rocks north of the Lincoln Mountain massif.

Moosalamoo Formation - quartzite member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Light-tan to gray, vitreous and non-vitreous quartzite and feldspathic quartzite and quartz conglomerate. Cover rocks of the Lincoln Mountain massif and northwestern flank of the Green Mountain massif.

Cheshire Quartzite - phyllite (Lower Cambrian) at surface, covers < 0.1 % of this area

Containing layers of dark-gray biotite-muscovite-quartz phyllite near top. Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

East Bethel plutons (Devonian) at surface, covers < 0.1 % of this area

Very light-bluish-gray to white, medium-grained, muscovite-biotite quartz monzonite, locally orbicular; commercially known as “Bethel white” and similar to the predominantly lighter-colored granitic rocks of southern Vermont. Part of other plutons of the New Hampshire Plutonic Suite.

Netop Formation - quartzite and quartz-pebble conglomerate (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Unit CZngs locally contains beds of grayish-green vitreous quartzite and quartz-pebble conglomerate, and thin beds of chloritic wacke, all shown as CZngq (unit is in part equivalent to rocks of the Mettawee slate facies and Zion Hill Quartzite Member of the Bull Formation). Rocks of the Dorset Mountain slice (includes Dorset Mountain proper and Mount Equinox, southward to West Mountain near Bennington). Part of the Taconic Allochthon.

Northfield Formation - quartzite, grit, and conglomerate member (Lower Devonian and Upper Silurian) at surface, covers < 0.1 % of this area

Dark-gray quartz-pebble metawacke and gray quartzite and conglomerate at base of the Northfield Formation, south of Springfield. Part of the Connecticut Valley Trough.

Ironbound Mountain Formation - amphibolite member (Lower Devonian) at surface, covers < 0.1 % of this area

Hornblende amphibolite and hornblende-plagioclase-quartz granofels; interpreted as metabasalt and mafic volcaniclastic rock. Part of the Connecticut Valley Trough.

Skeels Corners Slate - sandy matrix conglomerate member (Lower Ordovician and Cambrian) at surface, covers < 0.1 % of this area

Limestone and sandstone clasts in a quartz sand matrix. Cover rocks of the Saint Albans area.

Parker Slate - sandy dolostone member (Cambrian) at surface, covers < 0.1 % of this area

Sandy dolostone containing limestone clasts, interfingered with sandy dolostone containing dolostone clasts. Cover rocks of the Saint Albans area.

Parker Slate - sandstone member (Cambrian) at surface, covers < 0.1 % of this area

Thin- to thick-bedded calcareous coarse-grained sandstone. Cover rocks of the Saint Albans area.

Monadnock Mountain pluton - essexite (Middle Jurassic) at surface, covers < 0.1 % of this area

Pyroxene-biotite-hornblende andesine gabbroic rock grading into quartz syenite. Monadnock Mountain pluton: Composite stock of quartz syenite, syenite granite, and essexite. K-Ar age of 175±4 Ma (Foland and Faul, 1977). Part of the White Mountain Igneous Suite.

Mafic dikes (Neoproterozoic) at surface, covers < 0.1 % of this area

Medium- to coarse-grained, foliated, actinolite-chlorite-calcite-epidote retrograded metadiabasic dikes; commonly have relict diabasic texture. Cardinal Brook Intrusive Suite (965±4 Ma to 945±7 Ma). Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Underhill Formation - garnet schist (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Local lenses of garnet schist within the Underhill Formation. Cover rocks north of the Lincoln Mountain massif.

Pinney Hollow Formation - metafelsite member (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

White to pale-green, laminated to massive epidote-calcite-muscovite-quartz-albite metarhyolitic gneiss or schist; is a volcanic or volcaniclastic rock. U-Pb zircon age of 571±5 Ma, no. 21 (Walsh and Aleinikoff, 1999). Contains purplish-gray feldspathic quartzite. Cover rocks of Green Mountain anticlinorium.

Cram Hill Formation - feldspathic schist and granofels member (Middle? and Early Ordovician) at surface, covers < 0.1 % of this area

Medium-dark-gray to dark-gray, rusty-weathering garnet-biotite-muscovite-quartz-plagioclase schist and granofels; has coarse spangles of muscovite and locally is kyanite rich. Mapped in core of Spring Hill syncline. Part of the metasedimentary host rocks of the North River Igneous Suite. Cram Hill Formation: western part of the Cram Hill Formation is in part correlative with Whetstone Hill Member of the Moretown Formation. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Rowe Schist - graphitic schist and quartzite member (Cambrian and Neoproterozoic?) at surface, covers < 0.1 % of this area

Dark-gray- to sooty-gray-weathering, sulfidic, graphitic biotite-muscovite-plagioclase-quartz schist, containing thin beds of dark-bluish-gray vitreous quartzite. Restricted to minor occurrence in CZrch, along the base of the major amphibolite above CZrch, and within amphibolite at a structurally high position within the Rowe Schist near the Massachusetts State line. Closely resembles rocks typical of the Ottauquechee Formation but at a different structural or stratigraphic level. Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks. Rowe Schist: Mapped in southern Vermont where the uppermost part is continuous with amphibolites, schists, and feldspathic schists of the Rowe Schist of Massachusetts. These upper units are continuous with rocks of the Stowe Formation to the north. Units in the middle and lowermost structural positions (above the Hoosac Formation) are in a similar structural position as rocks of the Ottauquechee and Pinney Hollow Formations, although structural continuity and correlations with the Ottauquechee and Pinney Hollow Formations are uncertain owing to extensive structural duplication by thrust faulting and folding.

Mafic gneiss (Middle to Early Mesoproterozoic) at surface, covers < 0.1 % of this area

Dark-gray to black, fine-grained, magnetite-garnet-hornblende-biotite-diopside-plagioclase gneiss, commonly containing beds of dark-gray vitreous magnetite-garnet quartzite, 2 to 5 cm thick, tremolite-pyroxene gneiss, and biotite-rich, rusty-weathering garnet-quartz schist and gray sulfidic sillimanite quartzite. Occurs as screens within tonalitic gneiss and the Pharaoh Mountain Gneiss and is interpreted as paragneisses older than the tonalitic gneiss (Y2bt). Paragneiss. Rocks of the Adirondacks in Vermont and in the Whitehall, N.Y., area.

Ironbound Mountain Formation - Halls Stream Grit member (of Myers, 1964) (Lower Devonian) at surface, covers < 0.1 % of this area

Lenticular masses of coarse-grained quartzose volcaniclastic grit and cobble metaconglomerate commonly with abundant dark-gray metapelitic matrix (diamictite) interlayered with metasandstone, metapelite, and porphyritic metarhyolite. Grit contains subangular clasts of plagioclase and potassic feldspar as large as 2.5 cm across and larger clasts of dark-gray slate. Conglomerate contains rounded clasts of metarhyolite, fine-grained granitoid, and rare marble, and angular clasts of dark-gray slate. Part of the Connecticut Valley Trough.

Castleton Conglomerate (Cambrian and Neoproterozoic?) at surface, covers < 0.1 % of this area

Pods, lenses, or zones of thinly bedded limestone (ls), dolostone (d), and limestone conglomerate in the Mettawee slate facies in the Bull Formation, West Castleton Formation, and Hatch Hill Formation. These rocks locally contain Lower Cambrian fossils, but may range in age from Neoproterozoic to Late Cambrian. Includes named units shown locally as the North Brittain Conglomerate member of the West Castleton Formation (Cwcnb), the Bebe Limestone Member of the West Castleton Formation (Cwcbb), and the Castleton Conglomerate (of Shumaker and Thompson, 1967) (Cco). Rocks of the Giddings Brook, Sunset Lake, and Bird Mountain slices. Part of the Taconic Allochthon.

Rangeley Formation (Lower Silurian) at surface, covers < 0.1 % of this area

Interlayered, commonly rusty-weathering quartz-feldspar micaceous granofels and dark-gray mica schist containing porphyroblasts of garnet, staurolite, and kyanite. Calc-silicate lenses common in the granofels; granule and pebble metaconglomerate locally are present. Part of Piermont and other allochthons.

Quartzite and dolomitic quartzite (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Portion of unit CZbms locally containing light-gray, medium- to thick-bedded quartzite and dolomitic quartzite. Rocks of the Dorset Mountain slice (includes Dorset Mountain proper and Mount Equinox, southward to West Mountain near Bennington). Part of the Taconic Allochthon.

Stowe Formation - sericite schist member (Cambrian and Neoproterozoic?) at surface, covers < 0.1 % of this area

Quartz-sericite phyllite and schist. Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks.

Waits River Formation (Lower Devonian) at surface, covers < 0.1 % of this area

Interbedded medium- to dark-gray, moderately rusty weathering, highly contorted, unbedded schist and punky-weathering calcareous granofels or quartzose marble, and pods and stringers of vein quartz.

Goshen Formation (Lower Devonian) at surface, covers < 0.1 % of this area

Well-bedded micaceous quartzite or quartz schist grading upward into light- to dark-gray, carbonaceous aluminous schist in beds 5 to 15 cm thick.

Fort Ann Formation (Lower Ordovician) at surface, covers < 0.1 % of this area

(Shown only in New York State). Medium- to dark-gray and mottled, medium- to thick-bedded dolomitic limestone and buff-weathering dolostone. Part of the Beekmantown Group. Rocks of the Laurentian Margin. Part of the Adirondack lowlands and Lake Champlain lowlands (west of the Orwell and Champlain thrusts).

Compton Formation - amphibolite member (Lower Devonian) at surface, covers < 0.1 % of this area

Garnetiferous hornblende schist and minor hornblende amphibolite. Part of the Connecticut Valley Trough.

West Castleton Formation - Beebe Limestone member (Cambrian and Neoproterozoic?) at surface, covers < 0.1 % of this area

Pods, lenses, or zones of thinly bedded limestone (ls), dolostone (d), and limestone conglomerate in the Mettawee slate facies in the Bull Formation, West Castleton Formation, and Hatch Hill Formation. These rocks locally contain Lower Cambrian fossils, but may range in age from Neoproterozoic to Late Cambrian. Includes named units shown locally as the North Brittain Conglomerate member of the West Castleton Formation (Cwcnb), the Bebe Limestone Member of the West Castleton Formation (Cwcbb), and the Castleton Conglomerate (of Shumaker and Thompson, 1967) (Cco). Rocks of the Giddings Brook, Sunset Lake, and Bird Mountain slices. Part of the Taconic Allochthon.

Walloomsac Formation (Middle Ordovician) at surface, covers < 0.1 % of this area

Dark-gray, graphitic quartz phyllite and schist containing minor lenses of limestone.

Greenvale Cove Formation (Lower Silurian) at surface, covers < 0.1 % of this area

Thin-bedded muscovite-biotite-garnet-staurolite-kyanite schist and micaceous quartz-feldspar granofels; some calc-silicate lenses and layers. Part of Piermont and other allochthons.

Biotite-quartz-plagioclase paragneiss, amphibolite, and related migmatite (Middle Proterozoic) at surface, covers < 0.1 % of this area

Locally sillimanitic; commonly garnetiferous in and adjacent to Adirondack Highlands.

Ottauquechee Formation - coarse-muscovite schist member (Cambrian) at surface, covers < 0.1 % of this area

Silvery-green albite-chlorite-quartz-muscovite (±garnet) schist characterized by coarse muscovite porphyroblasts. Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks.

Hoosac Formation - schist member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Lustrous, dark-gray to silvery-gray tourmaline-muscovite-biotite-quartz schist and steel-gray muscovitic quartzite. Eastern flank of the Green Mountain massif and eastern domes.

Netop Formation - phyllite, dolostone and dolomitic quartzite (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Dark-gray phyllite containing bluish-gray dolostone and tan-weathering to locally mappable gray-weathering dolomitic quartzite. The Netop Formation may be in part equivalent in age and facies to parts of the West Castleton and Hatch Hill Formations, but may extend lower and into the Neoproterozoic. Rocks of the Dorset Mountain slice (includes Dorset Mountain proper and Mount Equinox, southward to West Mountain near Bennington). Part of the Taconic Allochthon.

Waits River Formation - Irasburg Conglomerate (member) (Lower Devonian and Upper Silurian) at surface, covers < 0.1 % of this area

Gray- to bluish-gray polymict limestone metaconglomerate containing pebbles to cobbles of limestone, pelite, granite, and intermediate to felsic volcanic rocks; also locally occurs in the Northfield Formation. Part of the Connecticut Valley Trough.

Hoosac Formation (Lower Cambrian and Proterozoic Z) at surface, covers < 0.1 % of this area

Rusty, gray, quartz-albite-mica (-chlorite) schist and gneiss. Locally conglomeratic.

Parker Slate - conglomerate member (Cambrian) at surface, covers < 0.1 % of this area

Conglomerate with dolostone and sandstone clasts in a shaly matrix. Cover rocks of the Saint Albans area.

Quartz schist (Early Mesoproterozoic) at surface, covers < 0.1 % of this area

Rusty-weathering sulfidic schist and minor amphibolite older than part of the South Londonderry Igneous Suite. Part of the aluminous schists and gneisses of the Washington Gneiss and Wilcox Formation and related rocks. Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Albitic biotite granite and pegmatite at Baker Brook (Late Mesoproterozoic) at surface, covers < 0.1 % of this area

Pinkish-gray garnet-biotite-albite pegmatite and granitic augen gneiss, distinguished by abundant rose-colored zircon; U-Pb zircon SHRIMP age of 1,037±6 Ma, no. 16 (Aleinikoff and others, 2011). Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Frontenac Formation, Graded-bedded metagraywacke and subordinate gray phyllite (Silurian?) at surface, covers < 0.1 % of this area

Frontenac Formation, Graded-bedded metagraywacke and subordinate gray phyllite.

Cuttingsville stock - essexite (Early Cretaceous) at surface, covers < 0.1 % of this area

Essexite (alkali gabbro). Part of the White Mountain Igneous Suite; Cuttingsville stock - Composite stock and intrusive breccia dikes consisting of augite and hastingsite syenite, nepheline and sodalite syenite, essexite, and monzodiorite. Associated dikes of monchiquite, camptonite, boston-ite, and spessartite. Average of five K-Ar ages 101 Ma; ages range between 103±4 and 99±2 Ma (Armstrong and Stump, 1971).

Rangeley Formation (Lower Silurian) at surface, covers < 0.1 % of this area

Within unit Sr; rusty sulfidic schist occurs in Fall Mountain nappe near Bellows Falls. Part of Piermont and other allochthons.

Fort Cassin Formation - Root Pond Quartzite Member (Middle and Lower Ordovician) at surface, covers < 0.1 % of this area

Light-gray to tannish-white, well-bedded and vitreous steel-gray quartzite interbedded with orangey-tan- and beige-weathering dolostone and thin beds of fossiliferous limestone. Named for occurrences near Root Pond in the Benson quadrangle, but herein extended to include thin lenses of quartzite that occur interbedded at several positions in the Fort Cassin Formation. Interbedded limestones contain upper Ibexian conodonts southwest of Root Pond (J.E. Repetski, USGS, written commun., 2004). Part of the Beekmantown Group. Rocks of the Laurentian Margin. Part of the Adirondack lowlands and Lake Champlain lowlands (west of the Orwell and Champlain thrusts).

Whitehall Formation - limestone (Lower Ordovician and Upper Cambrian) at surface, covers < 0.1 % of this area

Layers of gray limestone. Part of the Beekmantown Group. Rocks of the Laurentian Margin. Part of the Adirondack lowlands and Lake Champlain lowlands (west of the Orwell and Champlain thrusts).

Ottauquechee Formation - carbonate-bearing quartzite member (Cambrian) at surface, covers < 0.1 % of this area

Heterogeneous unit consisting of ankeritic greenstone, ankeritic or dolomitic muscovite quartzite, bluish-gray calcareous quartzite, and pods of brecciated dolostone. Exposed at Plymouth Five Corners. Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks.

Wilcox Formation - garnetiferous quartzite and quartz schist member (Middle Mesoproterozoic) at surface, covers < 0.1 % of this area

Lustrous muscovite-chlorite-chloritoid or muscovite-chlorite-biotite-clinozoisite retrograde schistose quartzite and large-garnet schist. Resembles a retrograde variety of the Hague Gneiss (of Alling, 1918) (Y2hgn) near Whitehall, N.Y. Part of the aluminous schists and gneisses of the Washington Gneiss and Wilcox Formation and related rocks. Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Partridge Formation - metarhyolite (Upper Ordovician) at surface, covers < 0.1 % of this area

Greenish-gray, light-bluish-gray, or medium-bluish-gray metarhyolite tuff, lapilli tuff, tuff breccia, and lava. Generally porphyritic with 5 to 20 percent plagioclase and, in some places, quartz phenocrysts and minor amphibolite. Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt.

Marble and calc-silicate gneiss (Middle Mesoproterozoic) at surface, covers < 0.1 % of this area

Medium-dark-gray to light-gray diopside-phlogopite-scapolite-calcite marble, phlogopite-tremolite-talc schist, and dark-gray diopside-hornblende (actinolite)-plagioclase calc-silicate gneiss. Paragneiss. Rocks of the Adirondacks in Vermont and in the Whitehall, N.Y., area.

Ascutney Mountain stock – tuffs (Early Cretaceous) at surface, covers < 0.1 % of this area

Trachytic to rhyolitic tuffs, and breccias containing fragments of volcanic rocks having trachytic flow structure and layering. Interpreted as volcanic rocks of the edifice. Part of the White Mountain Igneous Suite; Ascutney Mountain igneous complex - Consists of two plutons, a partial ring dike, and screens of volcanic rocks. K-Ar ages of 122 to 120 Ma (Foland and Faul, 1977).

Great Meadows Formation - limestone (Lower Ordovician) at surface, covers < 0.1 % of this area

Lens of light-gray- weathering fossiliferous limestone. Part of the Beekmantown Group. Rocks of the Laurentian Margin. Part of the Adirondack lowlands and Lake Champlain lowlands (west of the Orwell and Champlain thrusts).

Albee Formation - dark-gray slate and phyllite member (Ordovician and Cambrian) at surface, covers < 0.1 % of this area

Commonly sulfidic and rusty weathering. Indistinguishable from the Scarritt Member, but crops out in small areas. Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt.

Pegmatite dikes (Late Mesoproterozoic) at surface, covers < 0.1 % of this area

Pinkish-gray to light-gray, unfoliated, magnetite-biotite (±tourmaline) granite pegmatite, <1 m to 10 m thick. Crosscuts Ottawan foliation and locally fills narrow, northeast-trending, steeply dipping normal ductile shear zones. Intrusive rocks of the Adirondacks in Vermont and in the Whitehall, N.Y., area.

Tillotson Peak Structural Complex - pelitic schist (Cambrian) at surface, covers < 0.1 % of this area

Silvery-gray, medium-grained schist composed of white mica, quartz, chlorite (±garnet±albite±glaucophane±chloritoid); local centimeter-thick lenses of coticule. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Moretown Formation (Middle Ordovician or older) at surface, covers < 0.1 % of this area

Buff to gray, medium- to coarse-grained, poorly bedded mica-rich schist showing dark-green chlorite clots. Some pinstriped granofels.

Parker Slate - dark conglomerate member (Cambrian) at surface, covers < 0.1 % of this area

Conglomerate consisting of round clasts of orange dolostone in a black arenaceous matrix. Cover rocks of the Saint Albans area.

Ascutney Mountain stock - hornblende granite (Early Cretaceous) at surface, covers < 0.1 % of this area

Hornblende granite occurring as small intrusive masses in Kas. Part of the White Mountain Igneous Suite; Ascutney Mountain igneous complex - Consists of two plutons, a partial ring dike, and screens of volcanic rocks. K-Ar ages of 122 to 120 Ma (Foland and Faul, 1977).

Granite and Tonalite (Devonian) at surface, covers < 0.1 % of this area

Porphyritic, light-gray, hypabyssal biotite granite and tonalite in sill-like bodies - Contains phenocrysts of euhedral and embayed quartz, euhedral micro-cline with Carlsbad twinning (in granite), plagioclase, and euhedral biotite (±muscovite). Part of other plutons of the New Hampshire Plutonic Suite.

Cavendish Formation - calc-silicate member (Early Mesoproterozoic) at surface, covers < 0.1 % of this area

Coarse-grained dark-green diopside (±hornblende±zoisite)-calc-silicate rocks; white talc-tremolite (±dolomite)-calc-silicate schist; and minor quartzite, diopside quartzite, and schistose bluish-gray marble. Contains pods, stringers, and larger masses of granite pegmatite and interlayered aplitic gneiss. Marble and calc-silicate rocks are identical to units (Y2cs) within the biotite-quartz-plagioclase paragneiss member (Y1,2bg) of the Mount Holly Complex of the Green Mountain massif and eastern domes. Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes. The term “Cavendish Formation” is restricted to two belts of rocks within the Chester dome; the larger belt occurs at Cavendish and on Hawks Mountain, and a less extensive belt, containing similar rocks, occurs near Star Hill. An Early Mesoproterozoic age is here favored for the Cavendish Formation on the basis of (1) the presence of deformed pegmatite (Y3Cp) and areas of Felchville Gneiss (Y1fg and Y1fga) within the Cavendish and (2) the marked resemblance of members of the Cavendish to aluminous and feldspathic schists, calc-silicate rocks, and quartzites within the Mount Holly Complex. Similarities to rocks of the Hoosac Formation are also striking and cannot be altogether dismissed; however, the Hoosac Formation lacks pegmatite and contains distinctive and well-bedded albitic granofels, mafic volcanics, and coarse pebble-to-cobble conglomerate, all absent from the Cavendish. Zircons from a quartzite lens in dolomite marble at locality 4 have Pb-Pb ages between 1,290 and 934 Ma and suggest some of the marble of the Cavendish may be younger than the Felchville Gneiss (Karabinos and others, 1999). Retrograded muscovite-rich, chlorite-spotted, chloritoid-bearing quartz phyllites and garnet granofels and other rocks of the Wilcox Formation (Y2wxs) closely resemble those of the Cavendish Formation, as do chloritic-muscovitic retrograded Y2rs members of the Mount Holly Complex in the Green Mountain massif. Dolomite marble, talc-tremolite rock, diopside quartzite, calc-silicate gneiss, and lustrous chlorite-spotted, chlorite-muscovite-rich retrograded garnet gneiss and schist in the Mount Holly Complex contain abundant pegmatite (Y3Cp) on Blue Ridge Mountain in Chittenden and are identical but lower-grade correlatives of the Cavendish Formation. The coarse garnet-staurolite- and kyanite-bearing Gassetts Schist Member is interpreted to be an Acadian remetamorphosed product of the retrograde aluminous rocks now seen throughout the Mount Holly Complex of the Green Mountain massif and in the Pine Hill area.

Gile Mountain Formation - gri (Lower Devonian) at surface, covers < 0.1 % of this area

Lenticular masses of metamorphosed quartzose volcaniclastic grit and conglomerate, commonly having abundant dark-gray pelitic matrix interlayered with sandstone, pelite, and porphyritic rhyolite (Dgmr). Conglomerate contains rounded clasts of rhyolite, fine-grained granitoid, and angular clasts of dark-gray slate. Correlative with Halls Stream Grit Member of the Ironbound Mountain Formation (of Myers, 1964) to the north. Part of the Connecticut Valley Trough.

Monastery Formation - feldspathic quartzite (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Beds of gritty feldspathic quartzite. Unit mapped in Hancock and Ripton in part as lateral equivalent of the Tyson Formation to the south and the Underhill Formation to the north. Eastern flank of the Green Mountain massif and eastern domes.

Belvidere Mountain Structural Complex - spangly schist (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Silvery-blue, medium-grained tectonic mélange composed of muscovite schist with minor amounts of chlorite, epidote, albite, and tourmaline; contains fragments and discontinuous lenses of greenstone, coarse-grained amphibolite, and talc phyllite. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

West Castleton Formation - quartzite (Middle and Lower Cambrian) at surface, covers < 0.1 % of this area

Boudins of whitish-gray-weathering, bluish-gray quartzite. Rocks of the Giddings Brook, Sunset Lake, and Bird Mountain slices. Part of the Taconic Allochthon.

Stockbridge Formation (Lower Cambrian) at surface, covers < 0.1 % of this area

Beige, tan, and dark-gray weathering quartzose dolomite marble containing interbeds of black, green and maroon phyllite and punky weathering blue quartz pebble quartzite.

Stiles Pond pluton (Devonian) at surface, covers < 0.1 % of this area

Gray, medium-grained, nonfoliated biotite-muscovite tonalite. Part of other plutons of the New Hampshire Plutonic Suite.

Partridge Formation - amphibolite (Upper Ordovician) at surface, covers < 0.1 % of this area

Amphibolite. Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt.

Forestdale Formation - dolostone conglomerate (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

A boulder and cobble dolostone conglomerate. Cover rocks of the Lincoln Mountain massif and northwestern flank of the Green Mountain massif.

Stockbridge Formation (Lower Cambrian) at surface, covers < 0.1 % of this area

White to light-powdery-blue-gray dolostone with disseminated grains of quartz and prominent sprays of tremolite in higher-grade areas.

Fort Cassin Formation - Ward Siltstone Member (Lower Ordovician) at surface, covers < 0.1 % of this area

Light-tan to gray, thinly bedded and crossbedded, calcareous and dolomitic siltstone and quartzite in beds similar to the quartzite of the Root Pond Quartzite Member (Ofcrp). Part of the Beekmantown Group. Rocks of the Laurentian Margin. Part of the Adirondack lowlands and Lake Champlain lowlands (west of the Orwell and Champlain thrusts).

Cuttingsville stock - andesite breccia (Early Cretaceous) at surface, covers < 0.1 % of this area

Andesite breccia containing xenoliths of Mesoproterozoic gneiss and autoclasts of felsic alkalic and fine-grained mafic rocks. Part of the White Mountain Igneous Suite; Cuttingsville stock - Composite stock and intrusive breccia dikes consisting of augite and hastingsite syenite, nepheline and sodalite syenite, essexite, and monzodiorite. Associated dikes of monchiquite, camptonite, bostonite, and spessartite. Average of five K-Ar ages 101 Ma; ages range between 103±4 and 99±2 Ma (Armstrong and Stump, 1971).

Nassau Formation of Potter (1972) - Rensselaer Graywacke member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Nassau Formation of Potter (1972) - Rensselaer Graywacke member. Rocks of the Giddings Brook, Sunset Lake, and Bird Mountain slices. Part of the Taconic Allochthon.

Moretown Formation - mariposite-bearing metarodingite member (Lower Ordovician to Cambrian?) at surface, covers < 0.1 % of this area

Bright-green and white, fine- to medium-grained, variably foliated calcite-quartz-albite-mariposite-actinolite-tremolite-epidote-zoisite granofels to gneiss. Associated with greenstone and ultramafic rocks in Roxbury. Part of the metasedimentary host rocks of the North River Igneous Suite. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Dalton Formation (Lower Cambrian and Proterozoic Z) at surface, covers < 0.1 % of this area

Tan weathering, muscovite-microcline quartzite and feldspathic quartzite rich in black tourmaline, locally includes thin beds of other rock types listed below.

Stockbridge Formation (Lower Cambrian) at surface, covers < 0.1 % of this area

Massive to finely laminated steel-gray calcitic dolomite marble containing a prominent zone of white quartz nodules near top.

Austin Glen Graywacke (Upper Ordovician) at surface, covers < 0.1 % of this area

Unit is indistinguishable from beds in the Austin Glen Graywacke (after Potter, 1972) (Oag) interpreted as synorogenic autochthonous rocks. Rocks of the Giddings Brook, Sunset Lake, and Bird Mountain slices. Part of the Taconic Allochthon.

Diabase dikes (Neoproterozoic) at surface, covers < 0.1 % of this area

Dark-gray to greenish-gray, very fine grained, ocellar basaltic to medium-grained augite-plagioclase diabasic dikes, occurring as a subvertical northeast-trending discontinuous zone in the center of Bald Mountain. Intrusive rocks of the Adirondacks in Vermont and in the Whitehall, N.Y., area.

Gray, well-layered biotite-plagioclase-quartz gneiss (Proterozoic Y) at surface, covers < 0.1 % of this area

Containing beds of amphibolite, aluminous schist, quartzite, and calc-silicate gneiss.

Metagabbro (Middle Proterozoic) at surface, covers < 0.1 % of this area

Metagabbro, olivine metagabbro, derived amphibolite.

Frontenac Formation, undivided (Silurian?) at surface, covers < 0.1 % of this area

Interbedded thick feldspathic wackes, tan and green slates, and minor calcareous lenses.

Quartzite (Middle Mesoproterozoic) at surface, covers < 0.1 % of this area

Light-tan to yellowish-gray, massive to well-layered magnetite-garnet quartzite and magnetite-biotite-garnet quartzite in beds as much as 10 m thick. Occurs in two layers, one within or attached to the Hague Gneiss and one within biotite-quartz-plagioclase gneiss (Y2bpg) beneath the Hague Gneiss. The latter is rich in microcline and passes through interbedding into a quartzose facies of Y2bpg. Paragneiss. Rocks of the Adirondacks in Vermont and in the Whitehall, N.Y., area.

Nassau Formation (Lower Cambrian and Proterozoic Z) at surface, covers < 0.1 % of this area

Lustrous, soft green, yellowish-green and purple laminated chloritoid-chlorite phyllite (Mettawee Member).

Gile Mountain Formation - felsic metavolcanic member (Lower Devonian) at surface, covers < 0.1 % of this area

Very light gray, fine-grained porphyritic metafelsite schist or granofels near Maidstone Lake. Groundmass recrystallized to an aggregate of quartz, microcline, plagioclase, biotite, muscovite, and apatite; grain size about 0.05 mm. Relict phenocrysts of embayed quartz, microcline (some in granophyric intergrowths with quartz), and saussuritized plagioclase. U-Pb zircon age of 407.0±3.3 Ma, no. 45 (Rankin and Tucker, 2009). Part of the Connecticut Valley Trough.

Cheshire Quartzite (Lower Cambrian) at surface, covers < 0.1 % of this area

White, massive vitreous quartzite.

Gile Mountain Formation (Lower Devonian) at surface, covers < 0.1 % of this area

Gray, slightly rusty, poorly bedded phyllite and schist containing 20 cm to 2 m beds of light-gray, fine-grained quartzite, local punky-brown weathering calcareous granofels or quartzose marble, and pods and stringers of vein quartz.

Graptoliferous slate (Upper Ordovician) at surface, covers < 0.1 % of this area

Black slate of Climacograptus bicornis Biozone on and west of Whipstock Hill, otherwise typical of slates of the Walloomsac Formation shown as Ow. Part of the Taconic Allochthon.

Dolomite marble (Middle to Early Mesoproterozoic) at surface, covers < 0.1 % of this area

Beige to pinkish-gray-weathering, pyrite-bearing, medium- and fine-grained phlogopite-chlorite-dolomite marble exposed in cliffs east of the road at Devils Den. Grades into chlorite-biotite (±actinolite)-carbonate schist at structural base and has sharp contact with structurally overlying quartzite (Y?q). Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes. Unit is part of the Problematic rocks at Devils Den in Weston and Danby areas: Near Devils Den and Moses Pond includes albitic biotite-muscovite schist, chloritoid-chlorite-muscovite (±garnet) schist, dolomite marble and minor quartzite which resemble rocks of the Tyson Formation, and retrograde varieties of the paragneisses of the Mount Holly Complex. Because these rocks are structurally compatible with Grenvillian or older folds in the Mount Holly Complex and are transitional into rocks of the Mount Holly Complex, a Mesoproterozoic age is favored. Nevertheless the resemblance to rocks of the Tyson Formation is striking.

Hoosac Formation (Lower Cambrian and Proterozoic Z) at surface, covers < 0.1 % of this area

Green to gray-green chlorite-sericite-quartz phyllite; interbeds of chloritoid- or albite-rich schist and minor quartzite, locally rich in garnet and kyanite.

Brandon Lignite (Lower Miocene) at surface, covers < 0.1 % of this area

Organic silt, sand and gravel and slumped and dismembered lignite occurring as elongate disrupted deposits in underlying kaolin, residual hematite, and ochre deposits near Brandon. Lignite was let down into kaolin perhaps by karst collapse along a concealed west-dipping normal fault between the Dunham Dolostone on the west and the Cheshire Quartzite on the east. Deposit largely concealed but known from historic underground workings for kaolin, hematite ochre, and lignite.

Biotite metadiorite (Devonian) at surface, covers < 0.1 % of this area

Biotite metadiorite in unit Dgq northeast of St. Johnsbury - Medium-light-bluish-gray, fine-grained, foliated and lineated. Part of other plutons of the New Hampshire Plutonic Suite.

Cavendish Formation - Gassetts Schist member (Early Mesoproterozoic) at surface, covers < 0.1 % of this area

Lustrous, yellowish-grayish-green, ilmenite-staurolite (±kyanite)-garnet (large)-plagioclase-biotite-muscovite-quartz schist and warty-textured, dark-gray, biotite-rich garnet (large)-plagioclase-quartz schist. Passes locally into greenish, chlorite-spotted, magnetite-garnet (small)- plagioclase granofels in which large chlorite clots appear to replace earlier large garnet crystals. Unit closely resembles retrograded chlorite-spotted, biotite-garnet-plagioclase-quartz granofels and garnet-quartz-feldspar schist or gneiss of the Wilcox Formation of the Mount Holly Complex (Y2wsx). Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes. The term “Cavendish Formation” is restricted to two belts of rocks within the Chester dome; the larger belt occurs at Cavendish and on Hawks Mountain, and a less extensive belt, containing similar rocks, occurs near Star Hill. An Early Mesoproterozoic age is here favored for the Cavendish Formation on the basis of (1) the presence of deformed pegmatite (Y3Cp) and areas of Felchville Gneiss (Y1fg and Y1fga) within the Cavendish and (2) the marked resemblance of members of the Cavendish to aluminous and feldspathic schists, calc-silicate rocks, and quartzites within the Mount Holly Complex. Similarities to rocks of the Hoosac Formation are also striking and cannot be altogether dismissed; however, the Hoosac Formation lacks pegmatite and contains distinctive and well-bedded albitic granofels, mafic volcanics, and coarse pebble-to-cobble conglomerate, all absent from the Cavendish. Zircons from a quartzite lens in dolomite marble at locality 4 have Pb-Pb ages between 1,290 and 934 Ma and suggest some of the marble of the Cavendish may be younger than the Felchville Gneiss (Karabinos and others, 1999). Retrograded muscovite-rich, chlorite-spotted, chloritoid-bearing quartz phyllites and garnet granofels and other rocks of the Wilcox Formation (Y2wxs) closely resemble those of the Cavendish Formation, as do chloritic-muscovitic retrograded Y2rs members of the Mount Holly Complex in the Green Mountain massif. Dolomite marble, talc-tremolite rock, diopside quartzite, calc-silicate gneiss, and lustrous chlorite-spotted, chlorite-muscovite-rich retrograded garnet gneiss and schist in the Mount Holly Complex contain abundant pegmatite (Y3Cp) on Blue Ridge Mountain in Chittenden and are identical but lower-grade correlatives of the Cavendish Formation. The coarse garnet-staurolite- and kyanite-bearing Gassetts Schist Member is interpreted to be an Acadian remetamorphosed product of the retrograde aluminous rocks now seen throughout the Mount Holly Complex of the Green Mountain massif and in the Pine Hill area.

Hawley Formation (Middle Ordovician) at surface, covers < 0.1 % of this area

Interbedded amphibolite, greenstone, feldspathic schist and granofels. Coarse plagioclase in some amphibolite near top; local coarse hornblende blades or sprays. Sparse coticule (Emerson, 1917, p. 43). As used here the Hawley includes amphibolite, sulfidic rusty schists, abundant coticules, silvery schists, quartzites and quartz conglomerates, and quartz, feldspar, biotite granulites. The quartzites and quartz conglomerates occur at two positions in rocks here assigned to the Hawley. Those occurring near the top have been mapped previously as Russell Mountain Formation or as Shaw Mountain Formation. The Hawley overlies the Ordovician Barnard Gneiss and underlies Silurian and Devonian "calciferous schists" that include the westernmost Goshen Formation in MA and Northfield Formation in southern VT, the central Waits River Formation and the eastern Gile Mountain Formation. Authors believe that the Goshen, Northfield, and Waits River are facies equivalents, while the Gile Mountain is slightly younger. Map symbol indicates that Hawley is Ordovician and Silurian. 40Ar/3Ar hornblende release spectrum date of 433+/-3 Ma obtained by Spear and Harrison (1989) (Trzcienski and others, 1992).

Pinnacle Formation - heterogeneous unit (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Heterogeneous unit consists of coarse- to medium-grained clastic wacke, beige-weathering dolostone, and quartz-rich dolostone. Cover rocks of the Lincoln Mountain massif and northwestern flank of the Green Mountain massif.

Ironbound Mountain Formation, undivided (Lower Devonian) at surface, covers < 0.1 % of this area

Interbedded gray phyllite, in places containing feldspathic clasts, and feldspathic metasandstone, variably graded.

Forbes Hill conglomerate and breccia in the Ira and Hortonville Formations (Upper Ordovician) at surface, covers < 0.1 % of this area

Black slate containing angular to irregular chips of greenish-gray to yellowish-gray slate, quartz wacke, and limestone; interpreted by Zen (1961) as sedimentary wildflysch. Part of the Taconic Allochthon. Wildflysch-like conglomerates within the Hortonville, Ira, and Walloomsac Formations occur as local areas of black slate rich in inclusions of quartzite, greenish-gray slate, wacke, and punky-weathering bluish-gray limestone, interpreted as sedimentary breccias, deposited in front of the advancing Taconic allochthon (Upper Ordovician) (Zen, 1961; Potter, 1972; Fisher, 1985). Exposed near the western and northern margin of the allochthon and in the Bennington area at the type Whipstock. Here and at many localities the Forbes Hill and Whipstock breccias are tectonic breccias formed in situ by disruption of thin to thick beds, laminae, and carbonate-quartz-sulfide veins rather than clastic sedimentary rocks. The cleavage and related folding commonly is a late strain-slip cleavage characterized by a strong down-plunge lineation parallel to reclined hingelines of minor folds of foliation and compositional layering. Units are retained although interpretation as sedimentary wildflysch deposits is in part questionable.

Hawley Formation (Middle Ordovician) at surface, covers < 0.1 % of this area

Black, fine-grained, splintery, rusty-weathering schist and thin dark quartzite; interlayered amphibolite commonly has plagioclase megacrysts. As used here the Hawley includes amphibolite, sulfidic rusty schists, abundant coticules, silvery schists, quartzites and quartz conglomerates, and quartz, feldspar, biotite granulites. The quartzites and quartz conglomerates occur at two positions in rocks here assigned to the Hawley. Those occurring near the top have been mapped previously as Russell Mountain Formation or as Shaw Mountain Formation. The Hawley overlies the Ordovician Barnard Gneiss and underlies Silurian and Devonian "calciferous schists" that include the westernmost Goshen Formation in MA and Northfield Formation in southern VT, the central Waits River Formation and the eastern Gile Mountain Formation. Authors believe that the Goshen, Northfield, and Waits River are facies equivalents, while the Gile Mountain is slightly younger. Map symbol indicates that Hawley is Ordovician and Silurian. 40Ar/3Ar hornblende release spectrum date of 433+/-3 Ma obtained by Spear and Harrison (1989) (Trzcienski and others, 1992).

Highlandcroft Granodiorite of Billings (1935, 1937) (Early Silurian to Middle Ordovician) at surface, covers < 0.1 % of this area

Medium-greenish-gray to dark-greenish-gray, medium-grained, foliated metamorphosed granite, granodiorite, and tonalite containing quartz, microcline, saussuritized plagioclase, hornblende, biotite (chlorite alteration), and secondary calcite and sericite. Nonconformably overlain by the Clough Quartzite and Fitch Formation. U-Pb zircon age of 450±5 Ma, no. 28 (Lyons and others, 1986). Part of the Highlandcroft Plutonic Suite: Epizonal to mesozonal, foliated and metamorphosed (greenschist facies) plutons exposed northwest of the Ammonoosuc fault. Compositions range from granite to diorite to lesser amounts of gabbro. Part of the Bronson Hill arch intrusive rocks.

Felsic metavolcanic rocks (Silurian) at surface, covers < 0.1 % of this area

Includes volcanic debris flow, laminated tuff, and strongly foliated felsite. Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt.

Ironbound Mountain Formation, Grits at Halls Stream in northern New Hampshire (Lower Devonian) at surface, covers < 0.1 % of this area

Thickly bedded feldspathic volcaniclastic grit and interbedded gray slate. Equivalent to Grenier Ponds Member of the Ironbound Mountain Formation in western Maine.

Wilcox Formation - dolomite marble member (Middle Mesoproterozoic) at surface, covers < 0.1 % of this area

Beige-weathering to whitish-gray, fine-grained dolomite marble. Part of the aluminous schists and gneisses of the Washington Gneiss and Wilcox Formation and related rocks. Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Barber Hill stock - syenite (Early Cretaceous) at surface, covers < 0.1 % of this area

A small, 0.5-km-long, northwest-trending stock consisting of a coarse-grained alkali syenite core, a fine-grained quartz syenite border, and associated trachyte dikes (Kfd). K-Ar biotite age of 114±2 Ma (Armstrong and Stump, 1971). Part of the White Mountain Igneous Suite.

Ira Formation - conglomerate (Upper Ordovician) at surface, covers < 0.1 % of this area

A polymict limestone conglomerate. Unit mapped along east side of the Taconic allochthon south to Bennington. Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

Mafic gneiss (Middle Mesoproterozoic) at surface, covers < 0.1 % of this area

Screens, dikes, or sills of more mafic gneiss within unti Y2bt. Passes laterally into white, fine-grained trondhjemitic aplite near contacts with larger screens of paragneiss. U-Pb zircon Thermal Ionization Mass Spectrometry (TIMS) age of 1329±37 Ma (McLelland and Chiarenzelli, 1990) obtained from exposure 1.5 km west of Austin Hill on the west side of South Bay, west of Whitehall, N.Y. Contains lenses and screens of rusty sulfidic garnet-biotite-feldspar-quartz schist, dark-gray garnet-feldspar quartzite, and calc-silicate gneiss on south end of Austin Hill. Unit interpreted as intrusive into some paragneiss units that are here older than 1328±32 Ma (McLelland and Chiarenzelli, 1990). Rocks of the Adirondacks in Vermont and in the Whitehall, N.Y., area.

Moretown Formation (Middle Ordovician or older) at surface, covers < 0.1 % of this area

Nubble garnet schist, pinstriped granofels, and fine-grained amphibolite in equal parts.

Frontenac Formation - amphibolite member (Devonian and Silurian) at surface, covers < 0.1 % of this area

Garnetiferous hornblende schist and minor hornblende amphibolite. Part of the Connecticut Valley Trough.

West Castleton Formation - North Brittain Conglomerate member (Cambrian and Neoproterozoic?) at surface, covers < 0.1 % of this area

Pods, lenses, or zones of thinly bedded limestone (ls), dolostone (d), and limestone conglomerate in the Mettawee slate facies in the Bull Formation, West Castleton Formation, and Hatch Hill Formation. These rocks locally contain Lower Cambrian fossils, but may range in age from Neoproterozoic to Late Cambrian. Includes named units shown locally as the North Brittain Conglomerate member of the West Castleton Formation (Cwcnb), the Bebe Limestone Member of the West Castleton Formation (Cwcbb), and the Castleton Conglomerate (of Shumaker and Thompson, 1967) (Cco). Rocks of the Giddings Brook, Sunset Lake, and Bird Mountain slices. Part of the Taconic Allochthon.

Moretown Formation (Middle Ordovician or older) at surface, covers < 0.1 % of this area

Light-greenish-gray to buff, fine-grained, pinstriped granofels and schist.

Rowe Schist (Lower Ordovician and Cambrian) at surface, covers < 0.1 % of this area

Fine- to medium-grained, well-layered and foliated amphibolite; epidote-rich layers locally abundant. Includes its typical Chester Amphibolite Member at Chester, Massachusetts.

Dalton Formation - dolostone member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Buff, sandy, massive dolostone as lens in CZdph. Unit interfingers to the north with rocks of the Tyson Formation and to the east with rocks of the Hoosac Formation. Cover rocks of the Southern Green Mountains.

Littleton Formation (Lower Devonian) at surface, covers < 0.1 % of this area

Black to gray aluminous mica schist, quartzose schist, and aluminous phyllite.

Serpentinite (Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Brown-weathering, dark-green serpentinite. Part of Ultramafic rocks: occur as tectonic slivers and olistoliths in blocks within the Hazens Notch, Ottauquechee, Stowe, Rowe, and Moretown Formations. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.

Little Ascutney stock - paisanite dike (Early Cretaceous) at surface, covers < 0.1 % of this area

Fine-grained syenitic dike similar to spherulitic dikes found within the plutons and in the adjacent country rocks. One paisanite dike occurs well outside the Ascutney Mountain stocks in the saddle between the Chester and Athens domes. Part of the White Mountain Igneous Suite; Little Ascutney stock: A composite gabbro-diorite stock having two (eastern and western) intrusive centers defined by weakly developed igneous foliation. Gabbro is intruded by abundant, poorly defined areas of diorite. Includes two areas of syenite (Kas).

Dalton Formation (Lower Cambrian and Proterozoic Z) at surface, covers < 0.1 % of this area

Orangish-gray, gray, and light-greenish-gray muscovite-quartz schist and interlayered feldspathic quartzite and quartz conglomerate; minor beds of rusty albitic schist.

Stockbridge Formation (Lower Ordovician) at surface, covers < 0.1 % of this area

White to blue-gray and white layered calcite marble.

Dalton Formation (Lower Cambrian and Proterozoic Z) at surface, covers < 0.1 % of this area

Tan to orangish-tan quartz and gneiss cobble and pebble conglomerate, rusty feldspathic schist, and lustrous greenish-gray muscovite quartz schist.

Hoosac Formation (Lower Cambrian and Proterozoic Z) at surface, covers < 0.1 % of this area

Greenish chlorite-albite-magnetite-sericite-quartz schist and granofels.

Albee Formation - iron-formation member (Ordovician and Cambrian) at surface, covers < 0.1 % of this area

Ironstone, magnetite-rich rock and coticule. Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt.

Waits River Formation (Lower Devonian) at surface, covers < 0.1 % of this area

Amphibolite or hornblende schist locally containing conspicuous hornblende or garnet megacrysts. Rocks mapped as Conway Schist by Emerson (1898, 1917) and subsequently subdivided by Segerstrom (1956) and Willard (1956) were mapped across the MA-VT State line as Waits River and Gile Mountain Formations by Doll and others (1961) on Centennial Geologic Map of Vermont. Although controversy still exists over relative ages, detailed reconnaissance mapping by authors and S.F. Clark, Jr., L.M. Hall, and J.W. Pferd shows that Waits River and Gile Mountain Formations are readily distinguished in the field. For these reasons, and to maintain continuity across the State line, authors chose to follow VT nomenclature on here and on MA State bedrock geologic map (Zen and others, 1983). Primary difference between Waits River and Gile Mountain is presence in Gile Mountain of beds of noncalcareous, commonly micaceous quartzite. Both formations contain conspicuous beds of punky brown-weathering impure marble or calcareous granulite, mostly in Waits River and less abundant in Gile Mountain. Predominant lithology of both formations is typically contorted gray, graphitic, locally very sulfidic, moderately aluminous mica schist containing quartz veins. Gradational but definitely significant boundary can be mapped between both formations. Amphibolite in both formations may correlate with Standing Pond Volcanics occurring at or near Waits River-Gile Mountain contact in VT. Report goes into great detail regarding informal subdivision of each formation. Rocks previously mapped as Waits River Formation northeast of Shelburne Falls dome by Hatch and Hartshorn (1968) are here reassigned to an unnamed member of Goshen Formation because the rocks are indistinguishable from the Goshen. Goshen-Waits River contact is defined as the line along which, going eastward, the schist changes from aluminous, planar-bedded, and virtually quartz-free (Goshen), to alumina-poor, contorted, and rich in quartz veins (Waits River) (Hatch and others, 1988).

Sherman Marble (Proterozoic Y) at surface, covers < 0.1 % of this area

White, coarse-grained graphite dolomite-calcite marble at Sherman Reservoir at the State line.

Barber Hill stock - trachyte (Early Cretaceous) at surface, covers < 0.1 % of this area

Associated trachyte dikes of Kbh. Rb/Sr whole-rock isochron on trachyte dikes of 125±5 Ma (McHone and Corneille, 1980). Part of the White Mountain Igneous Suite.

Beekmantown Group (in part) (Cambrian) at surface, covers < 0.1 % of this area

In Champlain Valley: Whitehall Formation-dolostone, limestone (with Cryptozoon reefs); Ticonderoga Formation-dolostone (locally cherty), sandstone. In Vermont: Clarendon Springs Dolostone; Danby Formation-sandstone, quartzite, dolostone.

Carbonate - dolostone (Cambrian and Neoproterozoic?) at surface, covers < 0.1 % of this area

Pods, lenses, or zones of thinly bedded limestone (ls), dolostone (d), and limestone conglomerate in the Mettawee slate facies in the Bull Formation, West Castleton Formation, and Hatch Hill Formation. These rocks locally contain Lower Cambrian fossils, but may range in age from Neoproterozoic to Late Cambrian. Rocks of the Giddings Brook, Sunset Lake, and Bird Mountain slices. Part of the Taconic Allochthon.

Quartzite (Middle to Early Mesoproterozoic) at surface, covers < 0.1 % of this area

Light-gray to pinkish-gray, magnetite-muscovite-plagioclase quartzite at Devils Den. Grades into structurally overlying biotite-muscovite feldspathic schist and garnet-bearing feldspathic gneiss that contains pegmatite. Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes. Unit is part of the Problematic rocks at Devils Den in Weston and Danby areas: Near Devils Den and Moses Pond includes albitic biotite-muscovite schist, chloritoid-chlorite-muscovite (±garnet) schist, dolomite marble and minor quartzite which resemble rocks of the Tyson Formation, and retrograde varieties of the paragneisses of the Mount Holly Complex. Because these rocks are structurally compatible with Grenvillian or older folds in the Mount Holly Complex and are transitional into rocks of the Mount Holly Complex, a Mesoproterozoic age is favored. Nevertheless the resemblance to rocks of the Tyson Formation is striking.

Hortonville Formation - conglomerate (Upper Ordovician) at surface, covers < 0.1 % of this area

Locally a polymict limestone and dolostone-clast conglomerate. Unit mapped west of the Taconic allochthon, and northwest of the Sudbury slice. Vermont Valley sequence and Middlebury synclinorium (above the Orwell and Champlain thrusts).

Hawley Formation (Middle Ordovician) at surface, covers < 0.1 % of this area

Pale-buff, light-green or white, medium-grained plagioclase gneiss. As used here the Hawley includes amphibolite, sulfidic rusty schists, abundant coticules, silvery schists, quartzites and quartz conglomerates, and quartz, feldspar, biotite granulites. The quartzites and quartz conglomerates occur at two positions in rocks here assigned to the Hawley. Those occurring near the top have been mapped previously as Russell Mountain Formation or as Shaw Mountain Formation. The Hawley overlies the Ordovician Barnard Gneiss and underlies Silurian and Devonian "calciferous schists" that include the westernmost Goshen Formation in MA and Northfield Formation in southern VT, the central Waits River Formation and the eastern Gile Mountain Formation. Authors believe that the Goshen, Northfield, and Waits River are facies equivalents, while the Gile Mountain is slightly younger. Map symbol indicates that Hawley is Ordovician and Silurian. 40Ar/3Ar hornblende release spectrum date of 433+/-3 Ma obtained by Spear and Harrison (1989) (Trzcienski and others, 1992).

Gile Mountain Formation - quartz-pebble metaconglomerate member (Lower Devonian) at surface, covers < 0.1 % of this area

Thin lens of metadiamictite with abundant dark-gray, pyritic, and calcareous metapelite matrix at the base of the Meetinghouse Slate Member (Dgm), south of Bradford. Part of the Connecticut Valley Trough.

Retrograde gneiss (Mesoproterozoic) at surface, covers < 0.1 % of this area

Mylonitic chlorite-biotite-microcline-quartz gneiss, occurring as a sliver in the Shelburne Marble, South Wallingford. Part of the aluminous schists and gneisses of the Washington Gneiss and Wilcox Formation and related rocks. Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

Rowe Schist (Lower Ordovician and Cambrian) at surface, covers < 0.1 % of this area

Light-green to light-bluish-gray schist having thin granular quartz lenses and lamellae. Kyanite and staurolite typical at higher grades.

Quartzite, quartz-biotite schist and graphitic schist (Middle Proterozoic) at surface, covers < 0.1 % of this area

In part feldspathic, micaceous, garnetiferous, sillimanitic.

Goshen Formation (Lower Devonian) at surface, covers < 0.1 % of this area

Dg containing beds of punky-weathering calcareous granofels more than 15 cm thick near the contact with the Waits River Formation.