Geologic units in Franklin county, Vermont

Pinnacle Formation - undivided (Cambrian and Neoproterozoic) at surface, covers 21 % of this area

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

Fairfield Pond Formation (Cambrian and Neoproterozoic) at surface, covers 12 % of this area

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

Underhill Formation (Cambrian and Neoproterozoic) at surface, covers 10 % of this area

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

Hazens Notch Formation - undivided (Cambrian and Neoproterozoic) at surface, covers 8 % of this area

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

Iberville Formation (Upper Ordovician) at surface, covers 6 % of this area

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

Morses Line Slate (Ordovician) at surface, covers 5 % of this area

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

Jay Peak Formation - schist member (Cambrian and Neoproterozoic) at surface, covers 5 % of this area

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

Tibbit Hill Formation (Cambrian and Neoproterozoic) at surface, covers 5 % of this area

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

Skeels Corners Slate (Lower Ordovician and Cambrian) at surface, covers 5 % of this area

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

Cheshire Quartzite (Lower Cambrian) at surface, covers 4 % 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).

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).

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.

Parker Slate (Cambrian) at surface, covers 3 % of this area

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

Beekmantown Group, undivided (Middle Ordovician to Upper Cambrian) at surface, covers 1 % of this area

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

Cheshire Quartzite - argillaceous (Lower Cambrian) at surface, covers 1 % of this area

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

West Bridgewater Formation (Middle Ordovician) at surface, covers 1 % 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.

Sweetsburg Formation (Lower Ordovician and Cambrian?) at surface, covers 0.8 % of this area

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

Fayston Formation - albite schist member (Lower Cambrian and Neoproterozoic) at surface, covers 0.6 % 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.

Pinnacle Formation - amphibolitic greenstone member (Cambrian and Neoproterozoic) at surface, covers 0.6 % of this area

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

White Brook Formation (Cambrian and Neoproterozoic) at surface, covers 0.4 % of this area

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

Gorge Formation (Lower Ordovician and Cambrian) at surface, covers 0.4 % of this area

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

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

Glens Falls Limestone (Upper Ordovician) at surface, covers 0.3 % of this area

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

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

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

Highgate Formation (Lower Ordovician) at surface, covers 0.2 % of this area

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

Underhill Formation - quartzite, granofels, and metawacke (Cambrian and Neoproterozoic) at surface, covers 0.2 % of this area

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

Chazy Group - undivided (Upper and Middle Ordovician) at surface, covers 0.2 % of this area

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

Pinnacle Formation - feldspathic greenstone member (Cambrian and Neoproterozoic) at surface, covers 0.2 % of this area

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

Skeels Corners Slate - limestone matrix conglomerate member (Lower Ordovician and Cambrian) at surface, covers 0.2 % of this area

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

Pinnacle Formation - metabasalt and volcaniclastic rocks, undifferentiated (Cambrian and Neoproterozoic) at surface, covers 0.2 % of this area

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

Tillotson Peak Structural Complex - albite gneiss (Cambrian) at surface, covers 0.2 % of this area

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

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

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

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

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

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

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

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

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

Shelburne Marble (Lower Ordovician) at surface, covers < 0.1 % of this area

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

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

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

Cutting Dolostone (Lower Ordovician) at surface, covers < 0.1 % of this area

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

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

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

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

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

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

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

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

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

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

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

Chipman Formation - Bascom Formation (Middle and Lower Ordovician) at surface, covers < 0.1 % of this area

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

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

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

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

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

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

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

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.

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

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

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

Conglomerate consisting of round clasts of orange dolostone in a black arenaceous matrix. Cover rocks of the Saint Albans area.

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

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

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

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