Geologic units in Bennington county, Vermont

Netop Formation - chlorite phyllite member (Cambrian and Neoproterozoic) at surface, covers 10 % of this area

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

Biotite-quartz-plagioclase gneiss (Middle and Early Mesoproterozoic) at surface, covers 10 % 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.

Cheshire Quartzite (Lower Cambrian) at surface, covers 6 % of this area

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

Chipman Formation - Bascom Formation (Middle and Lower Ordovician) at surface, covers 6 % of this area

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

Biotite-granitic gneiss (Middle Mesoproterozoic) at surface, covers 6 % 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.

Bondville metadacite and trondhjemite gneiss (Middle Mesoproterozoic) at surface, covers 5 % of this area

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

Clarendon Springs Formation (Upper Cambrian) at surface, covers 5 % of this area

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

Carbonaceous phyllite and siltstone (Lower Cambrian and Neoproterozoic) at surface, covers 5 % of this area

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

Dunham Dolostone (Lower Cambrian) at surface, covers 4 % of this area

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

Rawsonville trondhjemite gneiss (Early Mesoproterozoic) at surface, covers 3 % 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.

Shelburne Marble (Lower Ordovician) at surface, covers 3 % of this area

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

Hoosac Formation - albite-quartz granofels member (Lower Cambrian and Neoproterozoic) at surface, covers 3 % 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.

Winooski Dolostone (Middle Cambrian) at surface, covers 3 % of this area

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

Walloomsac Formation (Upper Ordovician) at surface, covers 3 % of this area

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

Washington Gneiss (Middle Mesoproterozoic) at surface, covers 3 % of this area

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

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

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

Stamford Granite - rapakivi granite (Neoproterozoic) at surface, covers 2 % of this area

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

Nassau Formation of Potter (1972) - Mettawee member (Neoproterozoic) at surface, covers 2 % of this area

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

Bull Formation - Mettawee slate facies (Neoproterozoic) at surface, covers 1 % of this area

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

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

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

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

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

Monkton Quartzite (Middle Cambrian) at surface, covers 1 % of this area

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

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

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

Quartz schist and gneiss (Middle Mesoproterozoic) at surface, covers 1 % of this area

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

Netop Formation - phyllite and metasiltstone (Cambrian and Neoproterozoic) at surface, covers 1 % of this area

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

West Castleton and Hatch Hill(?) Formations - undifferentiated (Cambrian) at surface, covers 0.9 % of this area

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

Hornblende-plagioclase gneiss (Middle Mesoproterozoic) at surface, covers 0.8 % of this area

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

Dalton Formation - dark phyllite member (Lower Cambrian and Neoproterozoic) at surface, covers 0.8 % of this area

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

Hornblende diorite gneiss (Early Mesoproterozoic) at surface, covers 0.7 % of this area

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

Dalton Formation - conglomerate member (Lower Cambrian and Neoproterozoic) at surface, covers 0.7 % of this area

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

Felchville Gneiss - aplitic facies (Early Mesoproterozoic) at surface, covers 0.6 % of this area

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

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

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

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

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

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

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

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

Stamford Granite - aplitic granite (Neoproterozoic) at surface, covers 0.4 % of this area

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

Nassau Formation of Potter (1972) - Bomoseen Member (Neoproterozoic) at surface, covers 0.4 % of this area

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

Amphibolite (Early Mesoproterozoic) at surface, covers 0.3 % of this area

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

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

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

Dalton Formation - quartzite member (Lower Cambrian and Neoproterozoic) at surface, covers 0.2 % of this area

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

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

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

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

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

Quartzite - undifferentiated (Middle Mesoproterozoic) at surface, covers 0.2 % 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.

Calc-silicate rock (Middle Mesoproterozoic) at surface, covers 0.2 % 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.

College Hill Granite Gneiss (Middle Mesoproterozoic) at surface, covers 0.2 % of this area

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

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.

Whipstock Breccia in the Walloomsac Formation (Upper Ordovician) at surface, covers 0.2 % of this area

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

West Castleton Formation (Middle and Lower Cambrian) at surface, covers 0.1 % of this area

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

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

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

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.

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

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

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.

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

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

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

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

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

Undifferentiated Hoosac Formation.

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.

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

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

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

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

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

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

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

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

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

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

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

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

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.

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

Dark-gray, graphitic quartz phyllite and schist containing minor lenses of limestone.

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

Rusty, gray, quartz-albite-mica (-chlorite) schist and gneiss. Locally conglomeratic.

Albitic biotite granite and pegmatite at Baker Brook (Late Mesoproterozoic) at surface, covers < 0.1 % of this area

Pinkish-gray garnet-biotite-albite pegmatite and granitic augen gneiss, distinguished by abundant rose-colored zircon; U-Pb zircon SHRIMP age of 1,037±6 Ma, no. 16 (Aleinikoff and others, 2011). Mount Holly Complex intrusive rocks. Rocks of the Green Mountain and Lincoln Mountain massifs and eastern domes.

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

Dark-gray phyllite containing bluish-gray dolostone and tan-weathering to locally mappable gray-weathering dolomitic quartzite. The Netop Formation may be in part equivalent in age and facies to parts of the West Castleton and Hatch Hill Formations, but may extend lower and into the Neoproterozoic. Rocks of the Dorset Mountain slice (includes Dorset Mountain proper and Mount Equinox, southward to West Mountain near Bennington). Part of the Taconic Allochthon.

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

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

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

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

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

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

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

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

Stockbridge Formation (Lower Cambrian) at surface, covers < 0.1 % of this area

Beige, tan, and dark-gray weathering quartzose dolomite marble containing interbeds of black, green and maroon phyllite and punky weathering blue quartz pebble quartzite.

Stockbridge Formation (Lower Cambrian) at surface, covers < 0.1 % of this area

White to light-powdery-blue-gray dolostone with disseminated grains of quartz and prominent sprays of tremolite in higher-grade areas.

Nassau Formation of Potter (1972) - Rensselaer Graywacke member (Lower Cambrian and Neoproterozoic) at surface, covers < 0.1 % of this area

Nassau Formation of Potter (1972) - Rensselaer Graywacke member. Rocks of the Giddings Brook, Sunset Lake, and Bird Mountain slices. Part of the Taconic Allochthon.

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

Tan weathering, muscovite-microcline quartzite and feldspathic quartzite rich in black tourmaline, locally includes thin beds of other rock types listed below.

Stockbridge Formation (Lower Cambrian) at surface, covers < 0.1 % of this area

Massive to finely laminated steel-gray calcitic dolomite marble containing a prominent zone of white quartz nodules near top.

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

Lustrous, soft green, yellowish-green and purple laminated chloritoid-chlorite phyllite (Mettawee Member).

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

White, massive vitreous quartzite.

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

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

Graptoliferous slate (Upper Ordovician) at surface, covers < 0.1 % of this area

Black slate of Climacograptus bicornis Biozone on and west of Whipstock Hill, otherwise typical of slates of the Walloomsac Formation shown as Ow. Part of the Taconic Allochthon.

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

Green to gray-green chlorite-sericite-quartz phyllite; interbeds of chloritoid- or albite-rich schist and minor quartzite, locally rich in garnet and kyanite.

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.

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

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

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

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

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

Orangish-gray, gray, and light-greenish-gray muscovite-quartz schist and interlayered feldspathic quartzite and quartz conglomerate; minor beds of rusty albitic schist.

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

White to blue-gray and white layered calcite marble.

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

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

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

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

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

Tan to orangish-tan quartz and gneiss cobble and pebble conglomerate, rusty feldspathic schist, and lustrous greenish-gray muscovite quartz schist.

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

Greenish chlorite-albite-magnetite-sericite-quartz schist and granofels.

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

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

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

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