Geologic units in Windsor county, Vermont

Waits River Formation - carbonaceous phyllite and limestone member (Lower Devonian and Upper Silurian) at surface, covers 19 % of this area

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

Gile Mountain Formation - thick-bedded micaceous feldspathic quartzite member (Lower Devonian) at surface, covers 8 % of this area

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

Moretown Formation - “pinstriped” granofels member (Lower Ordovician to Cambrian?) at surface, covers 6 % 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.

Biotite-quartz-plagioclase gneiss (Middle and Early Mesoproterozoic) at surface, covers 6 % 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.

Waits River Formation - slate and phyllite member (Lower Devonian and Upper Silurian) at surface, covers 5 % 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.

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

Pinney Hollow Formation - phyllite member (Cambrian and Neoproterozoic) at surface, covers 3 % 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.

Baileys Mills tonalitic gneiss (Early Mesoproterozoic) at surface, covers 3 % of this area

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

Northfield Formation (Lower Devonian and Upper Silurian) at surface, covers 3 % 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.

Ottauquechee Formation - carbonaceous phyllite member (Cambrian) at surface, covers 3 % 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 (Middle Mesoproterozoic) at surface, covers 3 % 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.

Gile Mountain Formation - quartzite and metapelite member (Lower Devonian) at surface, covers 2 % of this area

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

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

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

Ammonoosuc Volcanics of Billings (1935) - metamorphosed andesitic and basaltic tuff, crystal tuff, and tuff breccia (Upper and Middle Ordovician) at surface, covers 2 % of this area

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

Moretown Formation - carbonaceous and sulfidic schist member (Lower Ordovician to Cambrian?) at surface, covers 2 % 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 - Whetstone Hill Member - phyllite facies (Lower Ordovician to Cambrian?) at surface, covers 2 % of this area

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

Barnard Gneiss proper (of Richardson, 1924) (Ordovician and Late Cambrian) at surface, covers 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 - chlorite schist member (Lower Ordovician to Cambrian?) at surface, covers 1.0 % 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.

Waits River Formation - mafic member (Lower Devonian and Upper Silurian) at surface, covers 1.0 % 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.

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.

Felchville Gneiss - trondhjemite facies (Early Mesoproterozoic) at surface, covers 0.9 % of this area

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

Moretown Formation - amphibolite and greenstone member (Lower Ordovician to Cambrian?) at surface, covers 0.9 % 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.

Felchville Gneiss - aplitic facies (Early Mesoproterozoic) at surface, covers 0.8 % 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.

Mixed felsic and mafic rocks (Ordovician and Late Cambrian) at surface, covers 0.8 % 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.

Gile Mountain Formation - Meetinghouse Slate member (Lower Devonian) at surface, covers 0.8 % 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.

Cavendish Formation - feldspathic schist and granofels member (Early Mesoproterozoic) at surface, covers 0.8 % of this area

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

Ottauquechee Formation - feldspathic schist and granofels member (Cambrian) at surface, covers 0.8 % 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.

Ottauquechee Formation - carbonaceous albite schist member (Cambrian) at surface, covers 0.7 % of this area

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

Moretown Formation - garnet schist member (Lower Ordovician to Cambrian?) at surface, covers 0.6 % 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.

Moretown Formation - hornblende fascicule schist and granofels member (Lower Ordovician to Cambrian?) at surface, covers 0.6 % 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.

Tyson Formation - chlorite-muscovite phyllite and schist member (Lower Cambrian and Neoproterozoic) at surface, covers 0.6 % 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.

Plymouth Formation - feldspathic quartzite member (Cambrian) at surface, covers 0.6 % 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.

Migmatitic gneiss (Middle Mesoproterozoic) at surface, covers 0.5 % 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.

Pinney Hollow Formation - amphibolite and greenstone member (Cambrian and Neoproterozoic) at surface, covers 0.5 % 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.

Fayston Formation - albite schist member (Lower Cambrian and Neoproterozoic) at surface, covers 0.5 % 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.

Ammonoosuc Volcanics of Billings (1935) - undivided (Upper and Middle Ordovician) at surface, covers 0.5 % 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.

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.

Ascutney Mountain stock – syenite (Early Cretaceous) at surface, covers 0.4 % of this area

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

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

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

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

Tyson Formation - quartz-pebble phyllite and wacke member (Lower Cambrian and Neoproterozoic) at surface, covers 0.4 % 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.

Tonalite gneiss (Early Mesoproterozoic) at surface, covers 0.3 % 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.

Little Ascutney stock - gabbro and diorite (Early Cretaceous) at surface, covers 0.3 % of this area

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

West Bridgewater Formation (Middle Ordovician) at surface, covers 0.3 % 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.

Moretown Formation - Whetstone Hill Member - metavolcanic facies (Lower Ordovician to Cambrian?) at surface, covers 0.3 % of this area

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

Waits River Formation - Garbenschiefer member (Lower Devonian and Upper Silurian) at surface, covers 0.3 % 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.

Waits River Formation - felsic volcanic member (Lower Devonian and Upper Silurian) at surface, covers 0.3 % 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.

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

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

Okemo Quartzite (Middle Mesoproterozoic) at surface, covers 0.3 % 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.

Proctor Hill granodiorite gneiss (Middle Mesoproterozoic) at surface, covers 0.3 % 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.

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

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

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

Hoosac Formation - undivided (Lower Cambrian and Neoproterozoic) at surface, covers 0.2 % 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.

Bull Hill Gneiss of Richardson (1931) (Neoproterozoic) at surface, covers 0.2 % 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 - feldspathic quartzite member (Lower Ordovician to Cambrian?) at surface, covers 0.2 % of this area

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

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

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

Cavendish Formation - marble member (Early Mesoproterozoic) at surface, covers 0.2 % of this area

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

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

Biotite-quartz diorite gneiss of Vernon dome (Late Ordovician) at surface, covers 0.2 % of this area

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

Rawsonville trondhjemite gneiss (Early Mesoproterozoic) at surface, covers 0.2 % 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.

Ascutney Mountain stock – hornfels (Early Cretaceous) at surface, covers 0.2 % of this area

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

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.

Amphibolite (Middle 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.

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

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

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

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.

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

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

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

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

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

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

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

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

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.

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.

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

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

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.

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.

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

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

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.

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

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

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.

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

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

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.

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.

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.

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

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

Partridge Formation (Upper Ordovician) at surface, covers < 0.1 % 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.

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.

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

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

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

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

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.

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

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

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

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

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 - albite-quartz granofels member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % 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.

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.

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.

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.

Bondville metadacite and trondhjemite gneiss (Middle Mesoproterozoic) at surface, covers < 0.1 % 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.

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

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

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

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

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.

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.

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.

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

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

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

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

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

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

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.

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.

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.

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

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

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.

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

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

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.

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

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

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

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

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

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

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.

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

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

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

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

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

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

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

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

Rowe Schist - chlorite phyllite member (Cambrian and Neoproterozoic?) at surface, covers < 0.1 % 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.

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

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

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

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

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

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

Silvery-green albite-chlorite-quartz-muscovite (±garnet) schist characterized by coarse muscovite porphyroblasts. Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks.

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

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

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.

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.

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

Heterogeneous unit consisting of ankeritic greenstone, ankeritic or dolomitic muscovite quartzite, bluish-gray calcareous quartzite, and pods of brecciated dolostone. Exposed at Plymouth Five Corners. Rocks of the Rowe-Hawley Zone. Allochthonous cover sequence east of the Green Mountains: rift and drift stage metasedimentary and metavolcanic rocks and tectonic inclusions of ultramafic rocks.

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

Trachytic to rhyolitic tuffs, and breccias containing fragments of volcanic rocks having trachytic flow structure and layering. Interpreted as volcanic rocks of the edifice. Part of the White Mountain Igneous Suite; Ascutney Mountain igneous complex - Consists of two plutons, a partial ring dike, and screens of volcanic rocks. K-Ar ages of 122 to 120 Ma (Foland and Faul, 1977).

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.

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.

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

Hornblende granite occurring as small intrusive masses in Kas. Part of the White Mountain Igneous Suite; Ascutney Mountain igneous complex - Consists of two plutons, a partial ring dike, and screens of volcanic rocks. K-Ar ages of 122 to 120 Ma (Foland and Faul, 1977).

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

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

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.

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.

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

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

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

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

Rowe Schist - amphibolite and greenstone member (Cambrian and Neoproterozoic?) at surface, covers < 0.1 % 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.

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.

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.

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.

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

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

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

Lustrous, yellowish-grayish-green, ilmenite-staurolite (±kyanite)-garnet (large)-plagioclase-biotite-muscovite-quartz schist and warty-textured, dark-gray, biotite-rich garnet (large)-plagioclase-quartz schist. Passes locally into greenish, chlorite-spotted, magnetite-garnet (small)- plagioclase granofels in which large chlorite clots appear to replace earlier large garnet crystals. Unit closely resembles retrograded chlorite-spotted, biotite-garnet-plagioclase-quartz granofels and garnet-quartz-feldspar schist or gneiss of the Wilcox Formation of the Mount Holly Complex (Y2wsx). Mount Holly Complex paragneiss. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes. The term “Cavendish Formation” is restricted to two belts of rocks within the Chester dome; the larger belt occurs at Cavendish and on Hawks Mountain, and a less extensive belt, containing similar rocks, occurs near Star Hill. An Early Mesoproterozoic age is here favored for the Cavendish Formation on the basis of (1) the presence of deformed pegmatite (Y3Cp) and areas of Felchville Gneiss (Y1fg and Y1fga) within the Cavendish and (2) the marked resemblance of members of the Cavendish to aluminous and feldspathic schists, calc-silicate rocks, and quartzites within the Mount Holly Complex. Similarities to rocks of the Hoosac Formation are also striking and cannot be altogether dismissed; however, the Hoosac Formation lacks pegmatite and contains distinctive and well-bedded albitic granofels, mafic volcanics, and coarse pebble-to-cobble conglomerate, all absent from the Cavendish. Zircons from a quartzite lens in dolomite marble at locality 4 have Pb-Pb ages between 1,290 and 934 Ma and suggest some of the marble of the Cavendish may be younger than the Felchville Gneiss (Karabinos and others, 1999). Retrograded muscovite-rich, chlorite-spotted, chloritoid-bearing quartz phyllites and garnet granofels and other rocks of the Wilcox Formation (Y2wxs) closely resemble those of the Cavendish Formation, as do chloritic-muscovitic retrograded Y2rs members of the Mount Holly Complex in the Green Mountain massif. Dolomite marble, talc-tremolite rock, diopside quartzite, calc-silicate gneiss, and lustrous chlorite-spotted, chlorite-muscovite-rich retrograded garnet gneiss and schist in the Mount Holly Complex contain abundant pegmatite (Y3Cp) on Blue Ridge Mountain in Chittenden and are identical but lower-grade correlatives of the Cavendish Formation. The coarse garnet-staurolite- and kyanite-bearing Gassetts Schist Member is interpreted to be an Acadian remetamorphosed product of the retrograde aluminous rocks now seen throughout the Mount Holly Complex of the Green Mountain massif and in the Pine Hill area.

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.

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.

Little Ascutney stock - paisanite dike (Early Cretaceous) at surface, covers < 0.1 % of this area

Fine-grained syenitic dike similar to spherulitic dikes found within the plutons and in the adjacent country rocks. One paisanite dike occurs well outside the Ascutney Mountain stocks in the saddle between the Chester and Athens domes. Part of the White Mountain Igneous Suite; Little Ascutney stock: A composite gabbro-diorite stock having two (eastern and western) intrusive centers defined by weakly developed igneous foliation. Gabbro is intruded by abundant, poorly defined areas of diorite. Includes two areas of syenite (Kas).

Barber Hill stock - trachyte (Early Cretaceous) at surface, covers < 0.1 % of this area

Associated trachyte dikes of Kbh. Rb/Sr whole-rock isochron on trachyte dikes of 125±5 Ma (McHone and Corneille, 1980). Part of the White Mountain Igneous Suite.

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

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

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

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