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

Geologic units in Washington county, Vermont

Gile Mountain Formation (Devonian) at surface, covers 6 % 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

Underhill Formation, Mount Abraham Schist Member (Cambrian) at surface, covers 1 % of this area

Underhill Formation, Mount Abraham Schist Member - Light gray sericite (muscovite-paragonite)-quartz-chloritoid rock with silvery sheen; porphyroblasts of magnetite are common and porphyroblasts of chlorite, chloritoid, garnet, and kyanite occur locally. (Northern and Central Vermont). Four distinctive units of Mount Abraham Schist occur within the Fayston-Buels Gore area, which are recognized on the basis of mineralogy, contact relationships, and geographic distribution. All are composed predominantly of white mica (muscovite and paragonite)-quartz-chlorite-chloritoid schist. One unit contains intraformational greenstone and metawacke; a second is a similar white mica schist but without the greenstone and metawacke; the third contains allanite; and the fourth, kyanite (Walsh, 1992).

Lithology: mica schist

Stowe Formation (Cambrian-Ordovician) at surface, covers 13 % 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

Undifferentiated Granitic Gneiss (Devonian) at surface, covers 7 % of this area

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

Lithology: granitic gneiss

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

Missisquoi Formation - Rusty weathering carbonaceous mica schist, quartzite and micaceous quartzite.

Lithology: mica schist; quartzite

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

Shaw Mountain Formation (Silurian) at surface, covers 0.3 % 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 (Cambrian) at surface, covers < 0.1 % of this area

Hazens Notch Formation - Interbedded carbonaceous and noncarbonaceous quartz-sericite-albite-chlorite schist; grades to quartzite and gneiss. (Northern and Central Vermont). According to author, the name Hazens Notch is a big problem in VT stratigraphic nomenclature. In northern VT, it consists of carbonaceous and non-carbonaceous schist associated with ultramafics, mafic schists, and blueschists, while in the Camels Hump quad, it is considered to be strictly a carbonaceous albitic schist with associated mafic schist. The use of the name Hazens Notch is not recommended for the white albitic schist of the Fayston-Buels Gore area. Those rocks are here assigned to the newly named Fayston Formation (Walsh, 1992).

Lithology: mica schist; quartzite; gneiss

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

Waits River Formation (Devonian) at surface, covers 26 % 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

Pinney Hollow Formation (Cambrian) at surface, covers 4 % of this area

Pinney Hollow Formation - Pale green quartz-sericite (muscovite-paragonite)-chlorite phyllite and schist with abundant magnetite, chloritoid phyllite and schist, quartz-sericite-albite-chlorite schist, and rare beds of carbonaceous and schistose quartzite; garnet porphyroblasts common south of Ottauquechee River. (Southern and Central Vermont).

Lithology: phyllite; mica schist; schist; quartzite

Pinney Hollow Formation, carbonaceous phyllite and schist (Cambrian) at surface, covers 9 % of this area

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

Lithology: phyllite; schist

Ultramafic Rocks (Ordovician) at surface, covers < 0.1 % of this area

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

Lithology: serpentinite; intrusive carbonatite

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

Ottauquechee Formation, Greenstone and Amphibolite. 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: greenstone; amphibolite

Northfield Formation (Devonian - Silurian) at surface, covers 3 % 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

Ottauquechee Formation (Cambrian) at surface, covers 3 % 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

Stowe Formation, greenstone and amphibolite (Cambrian-Ordovician) at surface, covers 3 % of this area

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

Lithology: greenstone; amphibolite

Underhill Formation, Battell Member (Cambrian) at surface, covers 0.1 % of this area

Underhill Formation, Battell Member - Carbonaceous sericite-quartz-albite-chlorite schist and schistose quartzite, also carbonaceous and noncarbonaceous limestone; quartz-sericite-chlorite-albite schist. (Northern and Central Vermont). The Battell is raised to Formation rank by T.R. Armstrong (in press) [not in bibliography] to describe graphitic schists with carbonates that depositionally overlie the Monastery Formation in the Granville-Hancock area of central VT. The name Battell Formation is tentatively assigned in this report to a distinct group of graphitic rocks with limited occurrence in the study area. The basal portion of the Battell is assigned by Armstrong to the White River Member (new name) and following that nomenclature, the White River is the only part of the Battell seen in the Fayston-Buels Gore area. The White River appears to be in fault contact with the Underhill Formation along the eastern boundary of the Underhill in Buels Gore. The member also appears to be in depositional contact with the Monastery Formation at all observed locations and occurs as small bodies within the schists of the Monastery (Walsh, 1992).

Lithology: mica schist; quartzite; limestone

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

Pinney Hollow Formation, Greenstone - Greenstone and actinolitic greenstone. (Southern and Central Vermont).

Lithology: greenstone

Missisquoi Formation, Harlow Bridge Quartzite Member (Ordovician) at surface, covers 0.5 % of this area

Missisquoi Formation, Harlow Bridge Quartzite Member - Buff to pale-green quartzite with interbeds of quartz-sericite-chlorite phyllite.

Lithology: quartzite; phyllite

Missisquoi Formation, Moretown Member (Ordovician) at surface, covers 17 % 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 0.2 % 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 5 % 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