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

Geologic units in Addison county, Vermont

Stowe Formation (Cambrian-Ordovician) at surface, covers 2 % 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

Underhill Formation, Mount Abraham Schist Member (Cambrian) at surface, covers 0.3 % 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

Middlebury and Chazy Limestone, Undifferentiated Youngman and Carman Formations, Crown Point Member (Ordovician) at surface, covers 1 % of this area

Middlebury and Chazy Limestone, Undifferentiated Youngman and Carman Formations, Crown Point Member - Massive, characterized by abundant Maclurites magnus.

Lithology: limestone

Hortonville, or Cumberland Head, and Glens Falls Formations, Undifferentiated (Ordovician) at surface, covers 8 % of this area

Hortonville, or Cumberland Head, and Glens Falls Formations, Undifferentiated - Hortonville or Cumberland Head is combined with Glens Falls where the boundary with the Glens Falls is widely covered by surficial deposits, also where the Cumberland Head thins.

Lithology: slate; phyllite; limestone; shale; conglomerate

Bascom Formation, and undifferentiated Luke Hill, Naylor Ledge and Hastings Creek Limestones (Ordovician) at surface, covers 4 % of this area

Bascom Formation, and undifferentiated Luke Hill, Naylor Ledge and Hastings Creek Limestones - Interbedded dolomite, limestone or marble, calcareous sandstone, quartzite and limestone breccia; irregular dolomitic layers, thin sandy laminae, and slaty or phyllitic partings characterize limestone and marble of lower, middle, and upper parts of the Bascom, respectively; south of West Rutland it includes some of the Chipman formation. The combined Luke Hill, Naylor Ledge, and Hastings Creek, east of Philipsburg thrust, are stratigraphically equivalent to the Bascom.

Lithology: dolostone (dolomite); limestone; marble; sandstone; quartzite; sedimentary breccia

Cutting Dolomite, and Undifferentiated Morgan Corner and Wallace Creek Formations (Ordovician) at surface, covers 3 % of this area

Cutting Dolomite, and Undifferentiated Morgan Corner and Wallace Creek Formations - Typical Cutting is a massive, gray weathered, nondescript dolomite with finely laminated calcareous sandstone at base. The combined Morgan Corner and Wallace Creek Formations, east of Philipsburg thrust, are stratigraphically equivalent to the Cutting. Cutting Formation of Cady (1945) is stratigraphically extended to include Division D, member 1 of Brainerd and Seeley, 1890, (now called Smith Basin Member), and is here renamed Cutting Hill Formation. No new type section is designated. Redefined unit includes Winchell Creek Sandstone Member, East Shoreham Member (named), and Smith Basin Member (Washington and Chisick, 1988).

Lithology: dolostone (dolomite); sandstone

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

Shelburne, Whitehall, and Strites Pond Formations (Ordovician) at surface, covers 2 % of this area

Shelburne, Whitehall, and Strites Pond Formations - The Shelburne is chiefly a white marble or gray limestone characterized by raised reticulate lines of gray dolomite on the weathered surface; includes Sutherland Falls marble, intermediate dolomite and Columbian marble of the marble quarries. Interbedded massive dolomite increases westward and predominates in the Whitehall formation, west of Champlain and Orwell thrusts. The Strites Pond, which is identical to the Shelburne, is east of Philipsburg thrust.

Lithology: marble; limestone; dolostone (dolomite)

Dunham Dolomite (Cambrian) at surface, covers 5 % of this area

Dunham Dolomite - Buff-weathered siliceous dolomite, pink and cream mottled or buff to gray on fresh surface; lower part is massive and upper part is sandy and resembles the Winooski Dolomite.

Lithology: dolostone (dolomite)

Stony Point Formation (Ordovician) at surface, covers 9 % of this area

Stony Point Formation - Predominantly calcareous black shale that grades upward into argillaceous limestone and rare dolomite beds, in northwestern Vermont.

Lithology: black shale; limestone; dolostone (dolomite)

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

Hortonville Formation - Black, carbonaceous and pyritic slate and phyllite, locally sandy; brown weathered limy beds are common near base. Occurs east of Highgate Springs, Champlain, and Orwell thrusts.

Lithology: slate; phyllite

Moosalamoo Phyllite (Cambrian) at surface, covers 0.5 % of this area

Moosalamoo Phyllite - Gray to black sericite-quartz phyllite; sericite-quartz-chlorite phyllite occurs locally.

Lithology: phyllite

St. Catherine Formation (Cambrian) at surface, covers 0.5 % of this area

St. Catherine Formation - Purple, gray-green, and variegated slate and phyllite containing minor interbeds of white to green quartzite; locally albitic. Purple and green chloritoid-bearing slate and phyllite is within dashed line in northern Taconic Range, but not separated farther south.

Lithology: slate; phyllite; quartzite

Monkton Quartzite (Cambrian) at surface, covers 5 % of this area

Monkton Quartzite - Distinctively red quartzite interbedded with lesser buff and white quartzite and relatively thick sections of dolomite like that of the Winooski; the quartzites thin to the east, and they become gray and phyllitic to the east and south.

Lithology: quartzite; dolostone (dolomite)

Chipman, Bridport, and Beldens Formations, Providence Island Dolomite; Burchards Member (Ordovician) at surface, covers 0.5 % of this area

Chipman, Bridport, and Beldens Formations, Providence Island Dolomite; Burchards Member - Blue-gray limestone with irregular spots of light buff dolomite that give weathered surface a mottled appearance.

Lithology: limestone; dolostone (dolomite)

Underhill Formation, Fairfield Pond Member (Cambrian) at surface, covers 1 % of this area

Underhill Formation, Fairfield Pond Member - Greenish quartzitic schist (quartz-sericite-albite-chlorite-biotite); sericite-quartz-chlorite phyllite, locally purple or red, common in lower part. (Northern and Central Vermont).

Lithology: mica schist; phyllite

Pinney Hollow Formation, carbonaceous phyllite and schist (Cambrian) at surface, covers 2 % of this area

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

Lithology: phyllite; schist

Chipman, Bridport, and Beldens Formations, Providence Island Dolomite; Bridport Dolomite Member (Ordovician) at surface, covers 3 % of this area

Chipman, Bridport, and Beldens Formation, Providence Island Dolomite; Bridport Dolomite Member - Buff to brown weathered, sharply defined and laterally persistent beds chiefly of medium bedded to massive, scored dolomite; variously designated Bridport Formation and Providence Island Dolomite in northwestern Vermont.

Lithology: dolostone (dolomite)

Chipman, Bridport, and Beldens Formations, Providence Island Dolomite; Beldens Member (Ordovician) at surface, covers 2 % of this area

Chipman, Bridport, and Beldens Formations, Providence Island Dolomite; Beldens Member - Interbedded buff to brown heavily scored dolomite and white to blue-gray marble and limestone; designated Beldens Formation east of Highgate Springs thrust.

Lithology: dolostone (dolomite); marble; limestone

Pinney Hollow Formation (Cambrian) at surface, covers 5 % 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

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

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

Cheshire Quartzite - Very massive, white to faintly pink or buff vitreous quartzite near the top in west-central and southwestern VT; predominantly a less massive appearing mottled gray, somewhat phyllitic quartzite; dolomitic sandstone and conglomerate near the base of the formation in west-central VT apparently grades southward into the Dalton Formation. Mapping in Bristol Notch and along the Green Mountain front indicate that the Cheshire Quartzite appears to be at least 2500 ft thick, which is about 2.5 times the original estimated thickness to the north and south. Near the base, the Cheshire is a massive argillaceous feldspathic meta-sandstone, containing recrystallized quartz and K-feldspar in a muscovite and biotite matrix. These lithologies grade upward through medium to thick-bedded schistose feldspathic meta-sandstones to clean, massive 'quartzites' of the Green Mountain front. Rocks currently mapped as the eastern-most Cheshire Quartzite probably belong to the Pinnacle Formation and are in fault contact with the Cheshire (Condon, 1993).

Lithology: quartzite; sandstone; conglomerate

Middlebury and Chazy Limestone; Undifferentiated Youngman and Carman Formations (Ordovician) at surface, covers 4 % of this area

Middlebury and Chazy Limestone, Undifferentiated Youngman and Carman Formations - Dark blue-gray, somewhat nodular and granular limestone with buff dolomite and shaly interbeds a fraction of an inch thick and 2 to 4 inches apart. The Middlebury, which is east of Champlain and Orwell thrusts, and the Youngman, which is east of Highgate Springs thrust, are, due partly to deformation, more slaty in appearance than the Chazy, which is west of the major thrusts. The Carman is a quartz sandstone with shaly partings that underlies the Youngman. The Chazy contains 3 members.

Lithology: limestone; dolostone (dolomite); shale; sandstone

Stowe Formation, greenstone and amphibolite (Cambrian-Ordovician) at surface, covers < 0.1 % of this area

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

Lithology: greenstone; amphibolite

Mount Holly Complex (Precambrian) at surface, covers 4 % of this area

Mount Holly Complex - Mainly fine- to medium-grained biotitic gneiss, locally muscovitic, and in western areas chloritic; massive and granitoid in some localities, fine-grained or schistose and compositionally layered in others; also abundant amphibolite and hornblende gneiss, and minor beds of mica schist, quartzite, and calc-silicate granulite; includes numerous small bodies of pegmatite and gneissoid granitic rock. Includes a suite of metatonalites, metatrondhjemite, and possible metadacite with chemical characteristics of a calc-alkaline volcanic-plutonic suite. Mappable units are College Hill Granite Gneiss and 10 unnamed subdivisions including several varieties of gneiss as well as schist, amphibolite, and quartzite. U-Pb zircon upper intercept ages of 1.35 to 1.30 Ga have been determined and interpreted as age of crystallization (Ratcliffe and others, unpub. data). Cores of abraded zircon obtained from College Hill Granite Gneiss of Mount Holly Complex have a U-Pb upper intercept age of 1245 +/-14 Ma, interpreted as crystallization age for that granite (Aleinikoff and others, 1990). Dust collected by abrasion of zircons, thought to represent migmatitic overgrowth, has a Pb-Pb age of approx 1100 Ma. These data suggest that College Hill Granite Gneiss was intruded at 1245 Ma and migmatized at 1100 Ma. On north and south slopes of College Hill, College Hill Granite Gneiss grades outward into migmatitic biotite granite gneiss of Mount Holly Complex. College Hill is discordant to contacts and folds in paragneiss units of Mount Holly Complex. Dacitic metavolcanics are found within Washington Gneiss of Berkshire massif of MA (Ratcliffe and Zartman, 1968). They are interbedded with thick succession of rusty-weathering, quartz-pebble gneisses, calc-silicate rocks and garnet-sillimanite schist similar to, but much thicker than, the rusty-weathering gneiss and schist unit of Mount Holly Complex exposed in Green Mountains of VT. It is possible that the metadacitic and metatrondhjemitic suite of VT constitutes a lateral, south-to-north facies of the Washington Gneiss of MA (Ratcliffe, in press).

Lithology: biotite gneiss; amphibolite; mafic gneiss; mica schist; quartzite; granulite; pegmatite; granite

Ottauquechee Formation (Cambrian) at surface, covers 1.0 % 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

Middlebury and Chazy Limestone, Undifferentiated Youngman and Carman Formations, Valcour Member (Ordovician) at surface, covers 0.4 % of this area

Middlebury and Chazy Limestone, Undifferentiated Youngman and Carman Formations, Valcour Member - Dark gray calcarenite succeeded by medium to light gray, buff-weathered silty, partly coquinal limestone.

Lithology: calcarenite; limestone

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

Underhill Formation, Forestdale Member buff to rusty weathered sandy dolomite and limestone. (Northern and Central Vermont).

Lithology: dolostone (dolomite); limestone

Hatch Hill and West Castleton Formations, Undifferentiated (Cambrian) at surface, covers < 0.1 % of this area

Hatch Hill and West Castleton Formations, Undifferentiated - The Hatch Hill, a relatively thin formation that succeeds the West Castleton, is characterized by rusty and spongy weathered gray calcareous quartzite traversed by numerous white-quartz viens. The West Castleton is a gray to black, siliceous, carbonaceous, and pyritiferous slate containing paper-thin white sandy laminae. Black slates are common to both formations. A blue-gray weathered black limestone is near the base of the West Castleton in a few places.

Lithology: quartzite; slate; limestone

Danby and Potsdam Formations (Cambrian) at surface, covers 2 % of this area

Danby and Potsdam Formations - The Danby is comprised of interbedded quartzite and dolomite; white quartzite beds, more than a foot thick, separated by 10 to 12 feet of dolomite in eastern areas, increase westward to continuous sections of white to pink weathered, massively bedded Potsdam quartzite, west of Orwell thrust.

Lithology: quartzite; dolostone (dolomite)

Clarendon Springs, Ticonderoga, and Rock River Dolomites; Gorge Formation (Cambrian) at surface, covers 1 % of this area

Clarendon Springs, Ticonderoga, and Rock River Dolomite; Gorge Formation - Fairly uniform, massive, smooth weathered gray dolomite characterized by numerous geodes and knots of white quartz; quartz sandstone and irregular masses of chert are near the top. Called the Ticonderoga west of Orwell and Champlain thrusts and the Rock River east of Philipsburg thrust. The Gorge is a partly conglomeratic facies on the west limb of the St. Albans synclinorium..

Lithology: dolostone (dolomite); sandstone; chert; conglomerate

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

Iberville Formation - Noncalcareous black shale interbedded with occasional dolomite beds and in the lower part with calcareous shale.

Lithology: black shale; dolostone (dolomite)

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

Mount Holly Complex, quartzite and schist (Precambrian) at surface, covers 0.9 % of this area

Mount Holly Complex, quartzite and schist - Quartzite, locally in massive beds as much as 30 ft thick, micaceous quartzite, and quartz-mica schist that commonly contains garnet or pseudomorphs (largely chlorite) after garnet; schists are locally rusty weathered and contain conspicuous flakes of graphite; also includes amphibolite and minor hornblende gneiss, biotite gneiss, and pegmatite.

Lithology: quartzite; mica schist; amphibolite; mafic gneiss; biotite gneiss; pegmatite

Mount Hamilton Formation (Ordovician) at surface, covers < 0.1 % of this area

Mount Hamilton Formation - White weatherd black, gray, green, purple, and red hard slates, some interbedded with thin cherty appearing quartzites and ribbon limestones a few vinches apart; smooth, soft, red slate; beds of ankeritic quartzite a few inches to several feet thick, locally containg layers of edgewise conglomerate; and a polymict limestone conglomerate. Lithic features vary laterally and are in many places indistinguishable from those of the underlying Hatch Hill and West Castleton Formations.

Lithology: slate; quartzite; limestone; conglomerate

Orwell Limestone and Isle la Motte and Lowville Limestones (Ordovician) at surface, covers 1 % of this area

Orwell Limestone and Isle la Motte and Lowville Limestones - Smooth ledged, sublithographic and lithographic, dove gray weathered limestone commonly cut by veins of white calcite; beds filled with fossil shell fragments are characteristic. The Lowville is a thin, undifferentieated unit near the base of the Orwell that is characteristically ashen gray and contains abundant Phytopsis tubulosum. The Isle La Motte is about the equivalent of the Orwell in areas west of Champlain thrust, on Isle La Motte and near South Hero, Highgate, Swanton, and St. Albans; it is locally underlain by the Lowville, which is too thin to show on map. The Sawyer Bay is herein defined as a member of the Lowville Formation of the Black River Group. Occurs approximately in the middle of the Lowville throughout the Champlain Valley and represents a significant deepening event. Lower part of the Lowville was deposited in a shallow lagoonal environment, while the Sawyer Bay was deposited in a subtidal normal marine environment. Deposition probably the result of high angle block faulting in the Champlain basin. Member is very dark gray to black micrite to sparite in composition with irregular "lumpy" bedding, wavy lamination, cross-lamination, and ripple marks. Irregularly shaped, scattered chert nodules are concentrated in specific horizons. Contains a few large and small brachiopods, trilobite fragments and some fossil hash. Member is approximately 6 ft thick at Sawyer Point, South Hero Island, northwestern VT; thins to 2 ft at Arnold Bay, and becomes an indistinct rubbly unit at Crown Point, northeastern NY. The Lowville, at Crown Point, also contains the House Creek Member. The House Creek is also present in northwestern NY, southern Ontario, and the Black River Valley, but is not seen at Sawyer Point or Arnold Bay. The Lowville reaches a maximum thickness of 50 ft at Crown Point and a minimum of 24 ft at Sawyer Point. The Lowville overlies the Pamelia Formation and underlies the Chaumont Formation. Age is Middle Ordovician (Blackriveran). (Bechtel and Mehrtens, 1995).

Lithology: limestone

Underhill Formation (Cambrian) at surface, covers 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

Forestdale Marble (Cambrian) at surface, covers < 0.1 % of this area

Forestdale Marble - Buff to rusty-weathered white, buff, and pink and white mottled dolomite containing local interbeds of dolomitic sandstone, gray-green phyllitic quartzite, and crossbedded sandy dolomite.

Lithology: marble; dolostone (dolomite); sandstone; quartzite

Glens Falls and Orwell Limestones, Undifferentiated (Ordovician) at surface, covers 0.6 % of this area

Glens Falls and Orwell Limestones, Undifferentiated - Combined where deformation has made the thin bedded Glens Falls undistinguishable from the thick bedded Orwell; from West Rutland south may contain rocks as low as the Middlebury.

Lithology: limestone; shale

Winooski Dolomite (Cambrian) at surface, covers 2 % of this area

Winooski Dolomite - Buff-weathered, pink, buff, and gray dolomite; beds 4 inches to 1 foot thick separated by thin, protruding, red, pink, green, and black siliceous partings.

Lithology: dolostone (dolomite)

Middlebury and Chazy Limestone, Undifferentiated Youngman and Carman Formations, Day Point Member (Ordovician) at surface, covers 0.2 % of this area

Middlebury and Chazy Limestone, Undifferentiated Youngman and Carman Formations, Day Point Member - Calcareous quartz sandstone, and calcarenite; orange-weathered dolomitic siltstones are common in eastern areas.

Lithology: sandstone; calcarenite; siltstone

Underhill Formation, Battell Member (Cambrian) at surface, covers 0.3 % 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

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

Hoosac Formation - Quartz-sericite-albite-biotite-chlorite schist characterized by albite porphyroblasts - biotite and garnet porphyroblasts common southward; locally carbonaceous. (Southern and Central Vermont). First revision is restriction of Tyson Formation and its replacement by Hoosac Formation in this quad. Cover rocks overlying basement of West River antiformal sheath fold (in hanging-wall of Ball Mountain thrust) consist of albitic schist locally containing pods of white dolomite and discontinuous basal beds of vitreous quartzite and interbedded dolomite as much as 15 m thick. These rocks were previously mapped as Tyson Formation by Doll and others (1961, State geologic map) and Karabinos (1984) and are now mapped as Hoosac Formation in this quad because of the presence of quartzite and dolomite locally contained within rusty albitic schist and granofels rocks typical of Hoosac. Similarly, cover rocks of Jamaica antiformal sheath fold consist of a 10-m-thick basal and quite continuous belt of dolomite marble that contains thin beds of vitreous quartzite. This unit was also mapped as Tyson by Doll and others (1961) and by Karabinos (1984) and is now mapped as Hoosac. Second revision is that Turkey Mountain Member is formalized as a member of Hoosac Formation to include all metabasalts within the formation. Exposed for a distance of 3 km northwest of Townshend. Consists of a collection of massive black amphibolite layers, 1 to 2 m thick, interlayered with epidotitic and quartz-rich, laminated greenstones. Total thickness of interbedded amphibolite and associated metasedimentary rock on Turkey Mountain is as much as 200 m. Termination of Turkey Mountain Member northward appears to result from thinning to the north although fault truncation along its lower contact cannot be ruled out. To the south, Turkey Mountain Member also appears to thin by interbedding with enclosing metasedimentary rocks, and pinches out north of Townshend. Where several layers in a limited region can be mapped separately, they are each referred to informally by use of subscripts in the letter symbol; this, however, does not imply correlation of numbered layers between different areas of the map (Ratcliffe, in press).

Lithology: mica schist

Pinnacle Formation (Cambrian) at surface, covers 8 % of this area

Pinnacle Formation - Schistose graywacke, gray to buff, commonly striped, quartz-albite-sericite-biotite-chlorite rock predominates; quartz-cobble and boulder conglomerate is common, chiefly near base. (Northern and Central Vermont).

Lithology: schist; conglomerate

Chipman, Bridport, and Beldens Formations, Providence Island Dolomite; Weybridge Member (Ordovician) at surface, covers 1 % of this area

Chipman, Bridport, and Beldens Formations, Providence Island Dolomite; Weybridge Member - Gray limestone with thin interbeds of sandy limestone 1/2 to 2 inches thick and 1 to 4 inches apart.

Lithology: limestone

Pinney Hollow Formation, Greenstone (Cambrian) at surface, covers 0.6 % of this area

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

Lithology: greenstone