Geologic units in Windham county, Vermont

Waits River Formation - carbonaceous phyllite and limestone member (Lower Devonian and Upper Silurian) at surface, covers 11 % of this area

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

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.

Northfield Formation (Lower Devonian and Upper Silurian) at surface, covers 5 % of this area

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

Hoosac Formation - albite-quartz granofels member (Lower Cambrian and Neoproterozoic) at surface, covers 5 % of this area

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

Biotite-granitic gneiss (Middle Mesoproterozoic) at surface, covers 4 % 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.

Waits River Formation - muscovite porphyroblastic carbonaceous schist member (staurolite-grade rocks) (Lower Devonian and Upper Silurian) at surface, covers 4 % of this area

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

Waits River Formation - slate and phyllite member (Lower Devonian and Upper Silurian) at surface, covers 3 % of this area

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

Bull Hill Gneiss of Richardson (1931) (Neoproterozoic) at surface, covers 3 % of this area

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

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

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

Harriman Reservoir Granite (Neoproterozoic) at surface, covers 3 % of this area

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

Rowe Schist - amphibolite and greenstone member (Cambrian and Neoproterozoic?) at surface, covers 3 % of this area

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

Rowe Schist - chlorite phyllite member (Cambrian and Neoproterozoic?) at surface, covers 2 % of this area

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

Moretown Formation - chlorite schist member (Lower Ordovician to Cambrian?) at surface, covers 2 % 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.

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

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

Moretown Formation - hornblende fascicule schist and granofels member (Lower Ordovician to Cambrian?) at surface, covers 2 % of this area

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

Rawsonville trondhjemite gneiss (Early Mesoproterozoic) at surface, covers 2 % 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.

Migmatitic gneiss (Middle Mesoproterozoic) at surface, covers 2 % 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.

Bondville metadacite and trondhjemite gneiss (Middle Mesoproterozoic) at surface, covers 1 % of this area

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

Hoosac Formation - albite schist and granofels member (Lower Cambrian and Neoproterozoic) at surface, covers 1 % of this area

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

Quartz schist and gneiss (Middle Mesoproterozoic) at surface, covers 1 % 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.

Hoosac Formation - Turkey Mountain metabasalt member (Lower Cambrian and Neoproterozoic) at surface, covers 1 % of this area

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

Branch Brook dike and sill complex - South Pond facies (Ordovician and Late Cambrian) at surface, covers 1 % of this area

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

Cram Hill Formation - gray quartz schist member (Middle? and Early Ordovician) at surface, covers 1 % of this area

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

Washington Gneiss (Middle Mesoproterozoic) at surface, covers 1 % of this area

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

Somerset Reservoir Granite - rapakivi granite and pegmatitic granite (Neoproterozoic) at surface, covers 1 % of this area

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

Gile Mountain Formation - Meetinghouse Slate member (Lower Devonian) at surface, covers 1 % of this area

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

Hoosac Formation - biotite phyllite member (Lower Cambrian and Neoproterozoic) at surface, covers 1 % of this area

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

Newfane tonalite (Ordovician and Late Cambrian) at surface, covers 1 % of this area

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

Branch Brook dike and sill complex - Whitneyville facies (Ordovician and Late Cambrian) at surface, covers 1 % of this area

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

Moretown Formation - carbonaceous and sulfidic schist member (Lower Ordovician to Cambrian?) at surface, covers 1 % of this area

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

Moretown Formation - garnet schist member (Lower Ordovician to Cambrian?) at surface, covers 1.0 % of this area

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

Rowe Schist - garnet schist member (Cambrian and Neoproterozoic?) at surface, covers 1.0 % of this area

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

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

Waits River Formation - quartzite and feldspathic quartzite member (Lower Devonian and Upper Silurian) at surface, covers 0.9 % of this area

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

Branch Brook dike and sill complex - Williamsville facies (Ordovician and Late Cambrian) at surface, covers 0.9 % of this area

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

Hoosac Formation - garnet schist member (Lower Cambrian and Neoproterozoic) at surface, covers 0.8 % of this area

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

Rowe Schist - Cooper Hill member (Cambrian and Neoproterozoic?) at surface, covers 0.8 % of this area

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

Oliverian Plutonic Suite - granodioritic to quartz dioritic gneissic (Late Ordovician) at surface, covers 0.7 % of this area

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

Waits River Formation - volcaniclastic rock member (Lower Devonian and Upper Silurian) at surface, covers 0.7 % of this area

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

College Hill Granite Gneiss (Middle Mesoproterozoic) at surface, covers 0.7 % of this area

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

Cram Hill Formation - amphibolite and greenstone member (Middle? and Early Ordovician) at surface, covers 0.7 % of this area

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

Waits River Formation - mafic member (Lower Devonian and Upper Silurian) at surface, covers 0.6 % of this area

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

Ammonoosuc Volcanics of Billings (1935) - undivided (Upper and Middle Ordovician) at surface, covers 0.6 % of this area

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

Rowe Schist - biotite-plagioclase schist and gneiss member (Cambrian and Neoproterozoic?) at surface, covers 0.6 % of this area

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

Hoosac Formation - garnet biotite schist member (Lower Cambrian and Neoproterozoic) at surface, covers 0.5 % of this area

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

Hornblende diorite gneiss (Early Mesoproterozoic) at surface, covers 0.5 % of this area

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

Dalton Formation - lustrous quartz schist member (Lower Cambrian and Neoproterozoic) at surface, covers 0.5 % 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.

Stowe Formation - schist and phyllite member (Cambrian and Neoproterozoic?) at surface, covers 0.4 % 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.

Hoosac Formation - chlorite albite schist and granofels member (Lower Cambrian and Neoproterozoic) at surface, covers 0.4 % of this area

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

Rawsonville trondhjemite gneiss - aplite (Early Mesoproterozoic) at surface, covers 0.3 % of this area

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

Rowe Schist - chlorite schist member (Cambrian and Neoproterozoic?) at surface, covers 0.3 % of this area

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

Cole Pond tonalite gneiss (Middle Mesoproterozoic) at surface, covers 0.3 % of this area

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

Amphibolite (Middle Mesoproterozoic) at surface, covers 0.3 % 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.

Northfield Formation - quartzose limestone (Lower Devonian and Upper Silurian) at surface, covers 0.3 % of this area

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

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

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

Meta-ultramafic rocks - undifferentiated (Cambrian and Neoproterozoic) at surface, covers 0.3 % 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.

Black Mountain pluton of the Guilford dome (Devonian) at surface, covers 0.3 % of this area

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

Somerset Reservoir Granite - aplitic to pegmatitic granite (Neoproterozoic) at surface, covers 0.2 % of this area

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

West Halifax Trondhjemite (Ordovician and Late Cambrian) at surface, covers 0.2 % of this area

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

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

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

Ruger Hill facies in the Spring Hill syncline (Ordovician and Late Cambrian) at surface, covers 0.2 % of this area

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

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

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

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.

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

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

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

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

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

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

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

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

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.

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

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

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

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

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

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

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

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

Pinney Hollow Formation - amphibolite and greenstone member (Cambrian and Neoproterozoic) at surface, covers 0.1 % 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.

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

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

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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.

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

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

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.

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

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

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

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

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.

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

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

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.

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

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

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

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

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

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

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

Undifferentiated Hoosac Formation.

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

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

Ottauquechee Formation - carbonaceous phyllite member (Cambrian) at surface, covers < 0.1 % 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.

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.

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

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

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

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

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

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

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

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

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

Lustrous, dark-gray to silvery-gray tourmaline-muscovite-biotite-quartz schist and steel-gray muscovitic quartzite. Eastern flank of the Green Mountain massif and eastern domes.

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

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

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

Within unit Sr; rusty sulfidic schist occurs in Fall Mountain nappe near Bellows Falls. Part of Piermont and other allochthons.

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.

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

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

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

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

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

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

Moretown Formation (Middle Ordovician or older) at surface, covers < 0.1 % of this area

Buff to gray, medium- to coarse-grained, poorly bedded mica-rich schist showing dark-green chlorite clots. Some pinstriped granofels.

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

Amphibolite. Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt.

Dalton Formation - undivided (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % 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.

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

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

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

Gray, slightly rusty, poorly bedded phyllite and schist containing 20 cm to 2 m beds of light-gray, fine-grained quartzite, local punky-brown weathering calcareous granofels or quartzose marble, and pods and stringers of vein quartz.

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

Interbedded amphibolite, greenstone, feldspathic schist and granofels. Coarse plagioclase in some amphibolite near top; local coarse hornblende blades or sprays. Sparse coticule (Emerson, 1917, p. 43). As used here the Hawley includes amphibolite, sulfidic rusty schists, abundant coticules, silvery schists, quartzites and quartz conglomerates, and quartz, feldspar, biotite granulites. The quartzites and quartz conglomerates occur at two positions in rocks here assigned to the Hawley. Those occurring near the top have been mapped previously as Russell Mountain Formation or as Shaw Mountain Formation. The Hawley overlies the Ordovician Barnard Gneiss and underlies Silurian and Devonian "calciferous schists" that include the westernmost Goshen Formation in MA and Northfield Formation in southern VT, the central Waits River Formation and the eastern Gile Mountain Formation. Authors believe that the Goshen, Northfield, and Waits River are facies equivalents, while the Gile Mountain is slightly younger. Map symbol indicates that Hawley is Ordovician and Silurian. 40Ar/3Ar hornblende release spectrum date of 433+/-3 Ma obtained by Spear and Harrison (1989) (Trzcienski and others, 1992).

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

Rusty-weathering sulfidic schist and minor amphibolite older than part of the South Londonderry Igneous Suite. Part of the aluminous schists and gneisses of the Washington Gneiss and Wilcox Formation and related rocks. Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

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

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

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

Black, fine-grained, splintery, rusty-weathering schist and thin dark quartzite; interlayered amphibolite commonly has plagioclase megacrysts. As used here the Hawley includes amphibolite, sulfidic rusty schists, abundant coticules, silvery schists, quartzites and quartz conglomerates, and quartz, feldspar, biotite granulites. The quartzites and quartz conglomerates occur at two positions in rocks here assigned to the Hawley. Those occurring near the top have been mapped previously as Russell Mountain Formation or as Shaw Mountain Formation. The Hawley overlies the Ordovician Barnard Gneiss and underlies Silurian and Devonian "calciferous schists" that include the westernmost Goshen Formation in MA and Northfield Formation in southern VT, the central Waits River Formation and the eastern Gile Mountain Formation. Authors believe that the Goshen, Northfield, and Waits River are facies equivalents, while the Gile Mountain is slightly younger. Map symbol indicates that Hawley is Ordovician and Silurian. 40Ar/3Ar hornblende release spectrum date of 433+/-3 Ma obtained by Spear and Harrison (1989) (Trzcienski and others, 1992).

Moretown Formation (Middle Ordovician or older) at surface, covers < 0.1 % of this area

Nubble garnet schist, pinstriped granofels, and fine-grained amphibolite in equal parts.

Gray, well-layered biotite-plagioclase-quartz gneiss (Proterozoic Y) at surface, covers < 0.1 % of this area

Containing beds of amphibolite, aluminous schist, quartzite, and calc-silicate gneiss.

Moretown Formation (Middle Ordovician or older) at surface, covers < 0.1 % of this area

Light-greenish-gray to buff, fine-grained, pinstriped granofels and schist.

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

Fine- to medium-grained, well-layered and foliated amphibolite; epidote-rich layers locally abundant. Includes its typical Chester Amphibolite Member at Chester, Massachusetts.

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

Black to gray aluminous mica schist, quartzose schist, and aluminous phyllite.

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

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

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

Amphibolite or hornblende schist locally containing conspicuous hornblende or garnet megacrysts. Rocks mapped as Conway Schist by Emerson (1898, 1917) and subsequently subdivided by Segerstrom (1956) and Willard (1956) were mapped across the MA-VT State line as Waits River and Gile Mountain Formations by Doll and others (1961) on Centennial Geologic Map of Vermont. Although controversy still exists over relative ages, detailed reconnaissance mapping by authors and S.F. Clark, Jr., L.M. Hall, and J.W. Pferd shows that Waits River and Gile Mountain Formations are readily distinguished in the field. For these reasons, and to maintain continuity across the State line, authors chose to follow VT nomenclature on here and on MA State bedrock geologic map (Zen and others, 1983). Primary difference between Waits River and Gile Mountain is presence in Gile Mountain of beds of noncalcareous, commonly micaceous quartzite. Both formations contain conspicuous beds of punky brown-weathering impure marble or calcareous granulite, mostly in Waits River and less abundant in Gile Mountain. Predominant lithology of both formations is typically contorted gray, graphitic, locally very sulfidic, moderately aluminous mica schist containing quartz veins. Gradational but definitely significant boundary can be mapped between both formations. Amphibolite in both formations may correlate with Standing Pond Volcanics occurring at or near Waits River-Gile Mountain contact in VT. Report goes into great detail regarding informal subdivision of each formation. Rocks previously mapped as Waits River Formation northeast of Shelburne Falls dome by Hatch and Hartshorn (1968) are here reassigned to an unnamed member of Goshen Formation because the rocks are indistinguishable from the Goshen. Goshen-Waits River contact is defined as the line along which, going eastward, the schist changes from aluminous, planar-bedded, and virtually quartz-free (Goshen), to alumina-poor, contorted, and rich in quartz veins (Waits River) (Hatch and others, 1988).

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

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

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

Pale-buff, light-green or white, medium-grained plagioclase gneiss. As used here the Hawley includes amphibolite, sulfidic rusty schists, abundant coticules, silvery schists, quartzites and quartz conglomerates, and quartz, feldspar, biotite granulites. The quartzites and quartz conglomerates occur at two positions in rocks here assigned to the Hawley. Those occurring near the top have been mapped previously as Russell Mountain Formation or as Shaw Mountain Formation. The Hawley overlies the Ordovician Barnard Gneiss and underlies Silurian and Devonian "calciferous schists" that include the westernmost Goshen Formation in MA and Northfield Formation in southern VT, the central Waits River Formation and the eastern Gile Mountain Formation. Authors believe that the Goshen, Northfield, and Waits River are facies equivalents, while the Gile Mountain is slightly younger. Map symbol indicates that Hawley is Ordovician and Silurian. 40Ar/3Ar hornblende release spectrum date of 433+/-3 Ma obtained by Spear and Harrison (1989) (Trzcienski and others, 1992).

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

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

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

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

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

Light-green to light-bluish-gray schist having thin granular quartz lenses and lamellae. Kyanite and staurolite typical at higher grades.

Sherman Marble (Proterozoic Y) at surface, covers < 0.1 % of this area

White, coarse-grained graphite dolomite-calcite marble at Sherman Reservoir at the State line.

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

Dg containing beds of punky-weathering calcareous granofels more than 15 cm thick near the contact with the Waits River Formation.