USGS Home
Contact USGS
Search USGS

Mineral Resources > Online Spatial Data > Geology > by state > Vermont Geology

Geologic units in Orleans county, Vermont

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

Shaw Mountain Formation - Quartzite, quartz conglomerate, cummingtonite schist, amphibolite, and quartz-sericite schist with porphyroblasts of biotite and garnet.

Lithology: quartzite; conglomerate; schist; amphibolite; mica schist

Hazens Notch Formation, Greenstone and Amphibolite (Cambrian) at surface, covers < 0.1 % of this area

Hazens Notch Formation, Greenstone and Amphibolite - Chiefly albite-actinolite-chlorite-epidote greenstone; locally hornblende-epidote-chlorite-albite amphibolite. (Northern and Central Vermont).

Lithology: greenstone; amphibolite

Undifferentiated Granitic Gneiss (Devonian) at surface, covers 17 % of this area

Undifferentiated Granitic Gneiss - Small dikes and sills do not show.

Lithology: granitic gneiss

Waits River formation, Standing Pond Volcanic Member (Devonian) at surface, covers < 0.1 % of this area

Waits River formation, Standing Pond Volcanic Member - Amphibolite, garnet amphibolite, coarse garnet schist with fasciculitic hornblende, and hornblende maculite; contains pillow lavas near St. Johnsbury and passes eastward into actinolitic greenstone and greenstone south of Windsor.

Lithology: amphibolite; schist; greenstone

Stowe Formation (Cambrian-Ordovician) at surface, covers 5 % of this area

Stowe Formation - Quartz-sericite (muscovite-paragonite)-chlorite phyllite and schist; porphyroblasts of albite, garnet, chloritoid, or kyanite common locally; includes phyllitic graywacke north of Lamoille River. Schist contains abundant segregations of granular white quartz. The Stowe Formation in the study are contains two unnamed members: a silvery green schist and a greenstone. The schist is a fine-grained, silvery to dark green quartz-muscovite-albite-chlorite schist. It is in fault contact with the black phyllite of the Ottauquechee Formation. The greenstone is a homogenous, fine-grained, light green actinolite-albite-epidote-calcite-chlorite schist. Large outcrops of the resistant greenstone are common. Age according to map symbols is Proterozoic and Cambrian. Unit is correlated with the Rowe Schist (of Zen, 1983). [Rowe Schist on 1983 MA map is Cambrian and Ordovician. No explanation here for older age.] (Walsh, 1992).

Lithology: phyllite; mica schist; graywacke

Stowe Formation, carbonaceous schist and phyllite (Cambrian-Ordovician) at surface, covers 1 % of this area

Stowe Formation, carbonaceous schist and phyllite - north of Lamoille River. Occurs in several small areas to the south, not shown on map.

Lithology: schist; phyllite

Ultramafic Rocks (Ordovician) at surface, covers 0.6 % of this area

Ultramafic Rocks - Dunite, peridotite, and serpentinite

Lithology: dunite; peridotite; serpentinite

Gile Mountain Formation (Devonian) at surface, covers 11 % of this area

Gile Mountain Formation - Gray quartz-muscovite phyllite or schist, interbedded and intergradational with gray micaceous quartzite (graywacke northeast of Nulhegan River), calcareous mica schist, and, locally, quartzose and micaceous crystalline limestone like that of the Waits River formation. The phyllite and schist commonly contain porphyroblasts of biotite, garnet, or staurolite, and locally kyanite, andalusite, or sillimanite. Used as Early Devonian Gile Mountain Formation. Generally consists of gray to tan metawacke and schist or phyllite, gradational into its Meetinghouse Slate Member, but much more thickly bedded and less pelitic. Contains minor metavolcanic lentils. Unnamed metavolcanic member is possibly equivalent to Putney Volcanics of southeastern VT. Separately mapped interbedded gray slate or phyllite and brown-weathering calcite-ankerite metasiltstone, and minor marble and quartzite, resembles Waits River Formation of VT. Meetinghouse Slate Member consists of gray to black phyllite and silty metasandstone turbidite. Report includes geologic map, cross sections, correlation chart, and four 1:500,000-scale derivative maps (Lyons and others, 1997).

Lithology: phyllite; mica schist; quartzite; limestone; graywacke

Missisquoi Formation, Coburn Hill Volcanic Member (Ordovician) at surface, covers 1 % of this area

Missisquoi Formation, Coburn Hill Volcanic Member - Actinolite-epidote-chlorite-albite greenstone and hornblende-albite-epidote amphibolite; includes pillow lavas.

Lithology: greenstone; amphibolite; metavolcanic rock

Waits River Formation, Ayers Cliff Member (Devonian) at surface, covers 6 % of this area

Waits River Formation, Ayers Cliff Member - Siliceous crystalline limestone containing thin beds of slate and phyllite north of the Lamoille River.

Lithology: limestone; slate; phyllite

Waits River Formation, Barton River Member (Devonian) at surface, covers 0.7 % of this area

Waits River Formation, Barton River Member - Interbedded siliceous crystalline limestone and sercite-quartz-chlorite phyllite in northern Vermont; diopsidic limestone and cordierite hornfels at contacts with granitic dikes and sills.

Lithology: limestone; phyllite; hornfels; granite

Missisquoi Formation, Moretown Member (Ordovician) at surface, covers 8 % of this area

Missisquoi Formation, Moretown Member - Quartzite and quartz-plagioclase granulite, in layers 1/8 to several inches thick, separated by "pinstripe" partings that contain muscovite, chlorite, epidote, biotite, and locally garnet; also greenish quartz-sericite-chlorite phyllite and schist, and minor carbonaceous phyllite. Schist and phyllite commonly contain biotite and garnet porphyroblasts in southern Vermont.

Lithology: granulite; quartzite; phyllite; schist

Missisquoi Formation, Cram Hill Member (Ordovician) at surface, covers 0.9 % of this area

Missisquoi Formation, Cram Hill Member - Pale greenish-gray to black phyllite grades locally into gray to black slate; felsic to mafic volcanic rocks.

Lithology: phyllite; slate; felsic metavolcanic rock; mafic metavolcanic rock

Underhill Formation (Cambrian) at surface, covers 0.4 % of this area

Underhill Formation - Silvery, gray-green, quartz-sericite-albite-chlorite-biotite schist, containing abundant lenticular segregations of granular white quartz; locally quartz-sercite-albite-chlorite phyllite; porphyroblasts of albite, garnet, and magnetite are common and locally very abundant in gneissic facies in axial anticlines of the Green Mountain anticlinorium . (Northern and Central Vermont). In study area consists mainly of greenish quartz-chlorite-sericite phyllites lying stratigraphically between Pinnacle and Cheshire Formations, where author would place rocks of type locality within Underhill facies of Pinnacle Formation, for they are clearly stratigraphically equivalent to rocks of Pinnacle Formation in Enosburg area, being below an excellent horizon marker, the Whitebrook dolomite and slate. However, Underhill facies of the Pinnacle and phyllites of Underhill Formation are practically indistinguishable in the field, and it is unavoidable, wherever dividing White Brook dolomite and slate are absent, to map all rocks of Underhill facies as one unit. In western part of outcrop belt, Underhill rocks are well defined between White Brook Dolomite or coarse Pinnacle graywacke below and Cheshire Formation above. Rocks in this clearly defined area are here recognized as Fairfield Pond Member. As mapped, the Underhill includes Fairfield Pond Member, Bakersfield Greenstone, Peaked Mountain Greenstone, White Brook Member, Jay Peak Member, and West Sutton Slate Member. Eastern facies of Underhill is named Bonsecours facies (Dennis, 1964).

Lithology: mica schist; phyllite

Missisquoi Formation, Umbrella Hill Member (Ordovician) at surface, covers 0.3 % of this area

Missisquoi Formation, Umbrella Hill Member - Quartz and slate pebble phyllitic conglomerate with interbeds of slate and phyllite - chiefly quartz-sericite-magnetite-chloritoid rocks.

Lithology: conglomerate; slate; phyllite

Underhill Formation, Jay Peak Member (Cambrian) at surface, covers 0.3 % of this area

Underhill Formation, Jay Peak Member - Pale, silver-green, quartz-sericite-chlorite-albite schist, locally quartzitic. (Northern and Central Vermont).

Lithology: mica schist; quartzite

Hazens Notch Formation, Belvidere Mountain Amphibolite Member (Cambrian) at surface, covers 0.4 % of this area

Hazens Notch Formation, Belvidere Mountain Amphibolite Member - Coarse- to fine-grained hornblende-epidote-albite rock; grades to epidote-chlorite-actinolite-albite greenstone where less metamorphosed. (Northern and Central Vermont).

Lithology: amphibolite; greenstone

Stowe Formation, greenstone and amphibolite (Cambrian-Ordovician) at surface, covers 0.3 % of this area

Stowe Formation, greenstone and amphibolite - Epidote-albite-chlorite rocks contain actinolite and hornblende where more metamorphosed.

Lithology: greenstone; amphibolite

Ottauquechee Formation (Cambrian) at surface, covers 2 % of this area

Ottauquechee Formation - Black carbonaceous phyllite or schist containing interbeds of massive quartzite commonly criss-crossed by veins of white quartz; quartzite is dark gray and carbonaceous, light gray, or white; also includes light green quartz-sericite-chlorite phyllite or schist and sercitic quartzite; beds of phyllitic graywacke and feldspar granule conglomerate are north of Lamoille River. Schist contains abundant porphyroblasts of garnet and biotite from Ludlow south. The Ottauquechee contains two major units: A black phyllite and the Thatcher Brook Member. The black phyllite contains a previously unreported sub-unit of gray carbonate schist. The Thatcher Brook Member (named in an abstract by Armstrong and others, 1988) is a carbonaceous albitic schist with greenstones and ultramafics. These rocks have previously been included in the Ottauquechee but have never been differentiated from the black phyllite. Member is in fault contact with the silvery green schist of the Pinney Hollow Formation to the west. Age is Cambrian (Ratcliff, in press).

Lithology: phyllite; schist; quartzite; graywacke; conglomerate

Pinney Hollow Formation, carbonaceous phyllite and schist (Cambrian) at surface, covers 11 % of this area

Pinney Hollow Formation, carbonaceous phyllite and schist. (Southern and Central Vermont).

Lithology: phyllite; schist

Waits River Formation (Devonian) at surface, covers 29 % of this area

Waits River Formation - Gray quartzose and micaceous crystalline limestone weathered to distinctive brown earthy crust; interbedded and intergradational with gray quartz-muscovite phyllite or schist. Where more metamorphosed the limestones contain actinolite, hornblende, zoisite, diopside, wollastonite, and garnet, and the phyllite and schist, biotite, garnet, and locally andalusite, kyanite or sillimanite.

Lithology: limestone; phyllite; mica schist

Northfield Formation (Devonian - Silurian) at surface, covers 1 % of this area

Northfield Formation - Dark gray to black quartz-sericite slate or phyllite with fairly widely-spaced interbeds a few inches thick of siltstone and silty crystalline limestone like that of the Waits River Formation; calcareous slate north of Lamoille River; phyllite passes into gray quartz-sericite schist containing abundant porphyroblasts of biotite and garnet in southern Vermont.

Lithology: slate; phyllite; mica schist; siltstone; limestone

Ultramafic Rocks (Ordovician) at surface, covers 0.2 % of this area

Ultramafic Rocks - Serpentinite, carbonate rock, talc-carbonate rocks and steatite.

Lithology: serpentinite; intrusive carbonatite

Underhill Formation, Greenstone (Cambrian) at surface, covers < 0.1 % of this area

Underhill Formation, Greenstone - varied composition including albite-chlorite-epidote-calcite and sericite-magnetite-chlorite-clinozoisite rocks. (Northern and Central Vermont).

Lithology: greenstone