Geologic units in Rutland county, Vermont

Bull Formation - Mettawee slate facies (Neoproterozoic) at surface, covers 19 % 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.

Biotite-quartz-plagioclase gneiss (Middle and Early Mesoproterozoic) at surface, covers 9 % 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.

Quartz schist and gneiss (Middle Mesoproterozoic) at surface, covers 5 % 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.

Winooski Dolostone (Middle Cambrian) at surface, covers 4 % 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).

West Castleton Formation (Middle and Lower Cambrian) at surface, covers 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.

Dunham Dolostone (Lower Cambrian) at surface, covers 3 % 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).

Cheshire Quartzite (Lower Cambrian) at surface, covers 3 % 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).

Ira Formation (Upper Ordovician) at surface, covers 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).

Hortonville Formation - shale and phyllite (Upper Ordovician) at surface, covers 3 % 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).

Poultney Formation (Middle and Lower Ordovician) at surface, covers 2 % 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.

West Castleton and Hatch Hill(?) Formations - undifferentiated (Cambrian) at surface, covers 2 % 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.

Pinney Hollow Formation - phyllite member (Cambrian and Neoproterozoic) at surface, covers 2 % 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.

Bull Formation - Bomoseen Graywacke member (Neoproterozoic) at surface, covers 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.

Biddie Knob Formation (Lower Cambrian and Neoproterozoic) at surface, covers 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.

Pawlet Formation (Upper Ordovician) at surface, covers 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.

Walloomsac Formation (Upper Ordovician) at surface, covers 1 % 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).

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).

Proctor Hill granodiorite gneiss (Middle Mesoproterozoic) at surface, covers 1 % 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.

Shelburne Marble (Lower Ordovician) at surface, covers 1 % 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).

Fayston Formation - albite schist member (Lower Cambrian and Neoproterozoic) at surface, covers 1 % 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.

Dalton Formation - undivided (Lower Cambrian and Neoproterozoic) at surface, covers 1 % 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.

Clarendon Springs Formation (Upper Cambrian) at surface, covers 1 % 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).

Forestdale Formation - dolostone member (Lower Cambrian and Neoproterozoic) at surface, covers 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.

Chipman Formation - Beldens Member (Middle Ordovician) at surface, covers 1.0 % 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).

Tyson Formation - quartz-pebble phyllite and wacke member (Lower Cambrian and Neoproterozoic) at surface, covers 1.0 % 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.

Whitehall Formation - dolostone (Lower Ordovician and Upper Cambrian) at surface, covers 0.9 % 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).

Pinnacle Formation - metawacke and phyllite member (Cambrian and Neoproterozoic) at surface, covers 0.9 % 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.

Microcline-augen granite and monzogranite gneiss (Late Mesoproterozoic) at surface, covers 0.9 % 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.

Wilcox Formation (Middle Mesoproterozoic) at surface, covers 0.9 % 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.

Biotite-granitic gneiss (Middle Mesoproterozoic) at surface, covers 0.9 % 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.

Quartzite - undifferentiated (Middle Mesoproterozoic) at surface, covers 0.8 % 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.

Hornblende-plagioclase gneiss (Middle Mesoproterozoic) at surface, covers 0.8 % 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.

Granitic gneiss of Chittenden Intrusive Suite (?) (Late Mesoproterozoic) at surface, covers 0.8 % 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.

Migmatitic gneiss (Middle Mesoproterozoic) at surface, covers 0.7 % 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.

Pinnacle Formation - metawacke member (Cambrian and Neoproterozoic) at surface, covers 0.6 % 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.

Middlebury Limestone (Middle Ordovician) at surface, covers 0.6 % 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).

Ludlow Mountain granodiorite gneiss (Middle Mesoproterozoic) at surface, covers 0.6 % 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.

Ottauquechee Formation - carbonaceous phyllite member (Cambrian) at surface, covers 0.5 % 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.

Calc-silicate rock (Middle Mesoproterozoic) at surface, covers 0.5 % 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.

Amphibolite (Middle Mesoproterozoic) at surface, covers 0.5 % 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.

Rawsonville trondhjemite gneiss (Early Mesoproterozoic) at surface, covers 0.5 % 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.

Dalton Formation - dark phyllite member (Lower Cambrian and Neoproterozoic) at surface, covers 0.4 % 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.

Danby Formation (Upper Cambrian) at surface, covers 0.4 % 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).

Granulose albitic gneiss (Mesoproterozoic?) at surface, covers 0.4 % 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.

Monkton Quartzite (Middle Cambrian) at surface, covers 0.4 % 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).

Dalton Formation - feldspathic quartzite member (Lower Cambrian and Neoproterozoic) at surface, covers 0.4 % 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.

Pharaoh Mountain Gneiss of Wiener and others (1984) (Late to Middle Mesoproterozoic) at surface, covers 0.3 % 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.

Tyson Formation - quartz phyllite member (Lower Cambrian and Neoproterozoic) at surface, covers 0.3 % 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.

Great Meadows Formation - dolostone (Lower Ordovician) at surface, covers 0.3 % 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).

Bull Formation - Zion Hill Quartzite member (Lower Cambrian and Neoproterozoic) at surface, covers 0.3 % 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.

Fort Cassin Formation (Middle and Lower Ordovician) at surface, covers 0.3 % 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).

Great Meadows Formation - Winchell Creek Member (Lower Ordovician) at surface, covers 0.3 % 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).

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

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

Ticonderoga Formation (Upper Cambrian) at surface, covers 0.3 % 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).

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).

Tyson Formation - conglomerate member (Lower Cambrian and Neoproterozoic) at surface, covers 0.2 % 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.

Chipman Formation - Weybridge Member (Middle Ordovician) at surface, covers 0.2 % 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).

Bird Mountain Grit of Dale (1900) (Lower Cambrian and Neoproterozoic) at surface, covers 0.2 % 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.

Stony Point Formation (Upper Ordovician) at surface, covers 0.2 % 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).

Tyson Formation - chlorite-muscovite phyllite and schist member (Lower Cambrian and Neoproterozoic) at surface, covers 0.2 % 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.

Ira Formation - limestone (Upper Ordovician) at surface, covers 0.2 % 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).

Tyson Formation - albite schist member (Lower Cambrian and Neoproterozoic) at surface, covers 0.2 % 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.

Netop Formation - chlorite phyllite member (Cambrian and Neoproterozoic) at surface, covers 0.2 % 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.

Equigranular granitic gneiss (Late Mesoproterozoic) at surface, covers 0.2 % 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.

Amphibolite (Early Mesoproterozoic) at surface, covers 0.2 % 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.

Biotite granite gneiss at Baker Brook (Mesoproterozoic) at surface, covers 0.2 % 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.

Cutting Dolostone (Lower Ordovician) at surface, covers 0.2 % 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).

Moosalamoo Formation - feldspathic quartzite and granofels member (Lower Cambrian and Neoproterozoic) at surface, covers 0.2 % 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.

Moosalamoo Formation - gray phyllite and metawacke member (Lower Cambrian and Neoproterozoic) at surface, covers 0.2 % 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.

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.

Orwell Limestone (Upper Ordovician) at surface, covers 0.2 % 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).

Stowe Formation - schist and phyllite member (Cambrian and Neoproterozoic?) at surface, covers 0.2 % 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.

Ludlow Mountain aplitic gneiss (Middle Mesoproterozoic) at surface, covers 0.2 % 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.

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.

Felchville Gneiss - aplitic facies (Early Mesoproterozoic) at surface, covers 0.2 % 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.

Tyson Formation - dolostone member (Lower Cambrian and Neoproterozoic) at surface, covers 0.2 % 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.

Biotite tonalite gneiss (Middle Mesoproterozoic) at surface, covers 0.2 % 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.

Indian River Slate (Upper Ordovician) at surface, covers 0.2 % 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.

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.

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.

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.

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.

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).

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.

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.

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.

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.

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).

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.

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).

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

Potsdam Sandstone (Covey Hill in Quebec)

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.

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).

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.

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.

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).

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.

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.

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.

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.

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.

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.

Moretown Formation - chlorite schist member (Lower Ordovician to Cambrian?) at surface, covers < 0.1 % 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.

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.

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.

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.

Glens Falls Limestone (Upper Ordovician) at surface, covers < 0.1 % 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).

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.

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.

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.

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.

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.

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.

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.

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.

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).

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.

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).

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.

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.

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.

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.

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.

Moretown Formation - “pinstriped” granofels member (Lower Ordovician to Cambrian?) at surface, covers < 0.1 % 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.

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).

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.

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.

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.

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.

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).

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.

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.

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.

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.

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).

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).

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).

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.

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).

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.

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.

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).

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.

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.

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.

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).

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.

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.

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).

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.

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.

Metagabbro (Middle Proterozoic) at surface, covers < 0.1 % of this area

Metagabbro, olivine metagabbro, derived amphibolite.

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.

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.

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.

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.

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.

Moretown Formation - Whetstone Hill Member - phyllite facies (Lower Ordovician to Cambrian?) at surface, covers < 0.1 % 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.

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.

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.

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.

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.

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.

Quartzite, quartz-biotite schist and graphitic schist (Middle Proterozoic) at surface, covers < 0.1 % of this area

In part feldspathic, micaceous, garnetiferous, sillimanitic.

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.

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.