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Geologic units in Vermont (state in United States)

[Additional scientific data in this geographic area]

Missisquoi Formation, Barnard Volcanic Member (Ordovician) at surface, covers 0.9 % of this area
Missisquoi Formation, Barnard Volcanic Member - Fine- to medium-grained biotite gneiss, hornblende gneiss, and amphibolite.
Lithology: biotite gneiss; mafic gneiss; amphibolite
Missisquoi Formation (Ordovician) at surface, covers 0.5 % of this area
Missisquoi Formation - Rusty weathering carbonaceous mica schist, quartzite and micaceous quartzite.
Lithology: mica schist; quartzite
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
Stowe Formation (Cambrian-Ordovician) at surface, covers 3 % 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, White Brook Member (Cambrian) at surface, covers < 0.1 % of this area
Underhill Formation, White Brook Member - Chiefly brown-weathered whitish, tan and gray sandy dolomite, locally only a hematitic zone; includes carbonaceous crystalline limestone in Cambridge syncline. (Northern and Central Vermont).
Lithology: dolostone (dolomite); limestone
Volcanic breccia, felsitic tuff, and flows. (Permian-Triassic) at surface, covers < 0.1 % of this area
Volcanic breccia, felsitic tuff, and flows.
Lithology: volcanic breccia (agglomerate); tuff; lava flow
Moretown Formation (Middle Ordovician or older) at surface, covers < 0.1 % of this area
Moretown Formation - Nubble garnet schist, pinstriped granofels, and fine-grained amphibolite in equal parts.
Lithology: schist; granofels; amphibolite
Gile Mountain Formation (Devonian) at surface, covers 10 % 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
Waits River Formation, Ayers Cliff Member (Devonian) at surface, covers 0.5 % 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
Essexitite (Permian-Triassic) at surface, covers < 0.1 % of this area
Essexitite
Lithology: gabbro
Cavendish Formation, Dolomite and Marble (Cambrian?) at surface, covers < 0.1 % of this area
Cavendish Formation, Dolomite and Marble - Buff dolomite; minor white to pink calcite marble; actinolitic and diopsidic marbles and beds of actinolite diopside granulite common in Chester dome. The Cavendish Formation is reinstated and considered part of the Mount Holly Complex in VT. Usage follows Thompson (1950), but is extended to include some rocks on Star Hill, including inner and outer cover rocks assigned by Downie (1982) to Hoosac and Pinney Hollow Formations. Formation is divided into four map units: calc-silicate rock and gneiss, marble, feldspathic schist or granofels, and the Gassetts Schist Member. The Cavendish correlates with the Wilcox Formation of the Mount Holly Complex in the Green Mountain massif, and therefore, is of Middle Proterozoic age (Ratcliffe, in press).
Lithology: dolostone (dolomite); marble; granulite
gneiss, quartzite, calc-silicate granulite (Precambrian) at surface, covers < 0.1 % of this area
Gneiss, quartzite, calc-silicate granulite.
Lithology: gneiss; quartzite; granulite
Beekmantown Group (in part) (Cambrian) at surface, covers < 0.1 % of this area
Beekmantown Group (in part) - In Champlain Valley: Whitehall Formation-dolostone, limestone (with Cryptozoon reefs); Ticonderoga Formation-dolostone (locally cherty), sandstone. In Vermont: Clarendon Springs Dolostone; Danby Formation-sandstone, quartzite, dolostone.
Lithology: dolostone (dolomite); limestone; sandstone; quartzite
Hortonville, or Cumberland Head, and Glens Falls Formations, Undifferentiated (Ordovician) at surface, covers 1.0 % 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
Partridge Formation, undivided (Middle - Upper Ordovician) at surface, covers < 0.1 % of this area
Partridge Formation, undivided - Black, rusty-weathering sulfidic-graphitic slate or schist and sparse to abundant metagraywacke. Lies stratigraphically between upper and lower parts of the Ammonoosuc Volcanics.
Lithology: slate; schist; metasedimentary rock
Sweetsburg Formation, Skeels Corners Slate and Mill River Conglomerate Members Undifferentiated (Cambrian) at surface, covers 0.4 % of this area
Sweetsburg Formation, Skeels Corners Slate and Mill River Conglomerate Members Undifferentiated - Black slate; local dolomite, sandstone, dolomite conglomerate, limestone bioherm, limestone, and calcareous shale. The Mill River is a basal limestone conglomerate.
Lithology: slate; dolostone (dolomite); sandstone; conglomerate; limestone; shale
Perry Mountain Formation, undivided (Lower? - Middle? Silurian) at surface, covers < 0.1 % of this area
Perry Mountain Formation, undivided - Sharply interbedded quartzites, light-gray nongraphitic metapelite, and "fast-graded" meta-turbidites. Coticule layers common.
Lithology: quartzite; meta-argillite; metasedimentary rock
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
Underhill Formation, Mount Abraham Schist Member (Cambrian) at surface, covers 0.1 % 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
Cavendish Formation, Bull Hill Gneiss (Cambrian?) at surface, covers 0.2 % of this area
Cavendish Formation, Bull Hill Gneiss - Quartz-plagioclase-microcline-biotite gneiss characterized in many areas by augen of microcline as much as 2 inches long; fine- to medium-grained quartz-plagioclase-biotite or biotite-muscovite gneiss. Cardinal Brook Intrusive Suite is here named in the cores of the Chester-Athens dome and Rayponda-Sadawga dome in the eastern and southern Green Mountains, VT, and the northern part of the Berkshire massif, MA. Includes the Stamford Granite of Hitchcock (1861), the Somerset Reservoir Granite (new name), the Harriman Reservoir Granite (new name), and the Bull Hill Gneiss of Richardson (1929-30). Because of uncertainty regarding the geologic position of the Bull Hill, it is restricted to the Chester and Athens domes and the original definition of Richardson is retained. Rocks mapped as Bull Hill in the Jamaica area are assigned to the Somerset Reservoir Granite and those in the Rayponda-Sadawga dome are assigned to the Harriman Reservoir Granite. Structural position is unclear. U-Pb zircon age is Middle Proterozoic (960-950 Ma). . [GNU Staff note--This report mistakenly uses the phrasing "Bull Hill Gneiss of Richardson (1929-30)" which would normally imply that the unit has not been adopted for use by the U.S. Geological Survey (USGS) because of inadequate definition by Richardson or successive workers in the area. However, in this report, the phrasing simply means that Richardson's definition and use are preferred over the usage on the VT State Geologic Map of Doll and others (1961) and that the unit meets the requirements for formal usage by the USGS.] (Ratcliffe, 1991).
Lithology: gneiss; biotite gneiss
Trondhjemite (Late Ordovician) at surface, covers < 0.1 % of this area
Trondhjemite - Contains biotite and hornblende.
Lithology: trondhjemite
Pinnacle Formation (Cambrian) at surface, covers 3 % 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
Madrid and Smalls Falls Formations, undivided (Silurian) at surface, covers < 0.1 % of this area
Madrid and Smalls Falls Formations, undivided.
Lithology: granofels; schist; calc-silicate schist; pelitic schist
Pinney Hollow Formation, Chester Amphibolite Member (Cambrian) at surface, covers 0.1 % of this area
Pinney Hollow Formation, Chester Amphibolite Member - Thin-layered, ligniform amphibolite and hornblende schist; includes actinolitic greenstone and greenstone north of Windham. (Southern and Central Vermont).
Lithology: amphibolite; amphibole schist; greenstone
Chipman, Bridport, and Beldens Formations, Providence Island Dolomite; Bridport Dolomite Member (Ordovician) at surface, covers 0.3 % 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)
Middlebury and Chazy Limestone, Undifferentiated Youngman and Carman Formations, Crown Point Member (Ordovician) at surface, covers 0.2 % of this area
Middlebury and Chazy Limestone, Undifferentiated Youngman and Carman Formations, Crown Point Member - Massive, characterized by abundant Maclurites magnus.
Lithology: limestone
Hathaway Formation (Ordovician) at surface, covers < 0.1 % of this area
Hathaway Formation - Gray to black argillite and bedded radiolarian chert, with included blocks and fragments of chert, limestone, dolomite, sandstone and graywacke.
Lithology: argillite; chert; limestone; dolostone (dolomite); sandstone; graywacke
Underhill Formation, carbonaceous quartz-sericite-albite-chlorite schist and phyllite. (Cambrian) at surface, covers < 0.1 % of this area
Underhill Formation, carbonaceous quartz-sericite-albite-chlorite schist and phyllite. (Northern and Central Vermont).
Lithology: mica schist; phyllite
Mount Holly Complex, calcite and dolomite marbles (Precambrian) at surface, covers < 0.1 % of this area
Mount Holly Complex, calcite and dolomite marbles - locally coarse grained; commonly contain phlogopite, actinolite, and diopside, and are interbedded with medium- to coarse-grained calc-silicate granulite; includes minor amounts of other types of Precambrian rock.
Lithology: marble; granulite; metamorphic rock
Cutting Dolomite, and Undifferentiated Morgan Corner and Wallace Creek Formations (Ordovician) at surface, covers 0.4 % 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
Tyson Formation (Cambrian) at surface, covers 0.2 % of this area
Tyson Formation - Feldspathic quartz-mica schist containing biotite, chlorite, and carbonate; many beds contain pebbles of quartz and feldspar; cobble or boulder conglomerate commonly at base; thin beds of quartzite, carbonaceous phyllite, and schistose dolomite in upper part, overlain at top by massive buff dolomite as much as 30 ft thick. (Southern and Central Vermont). The Tyson Formation contains grits and conglomerates at its base that unconformably overlie basement. The conglomerates and grits are as much as 150 m thick and contain lenses of dolomitic quartzite and feldspathic grit. Unit also contains black carbonaceous phyllite and interbedded dolostone as much as 100 m thick, followed by beige to tan weathering beds of dolostone that increase in abundance toward the top of the unit and pass into punky weathering dolomitic and feldspathic quartzite at the top. From a point near the southwest corner of the Andover quad, the rocks of the Tyson Formation are laterally replaced by albitic schists and granofels of the Hoosac Formation to the south. Therefore, Tyson laterally replaces the Hoosac from south to north along the eastern margin of the Green Mountain massif. The Tyson Formation is of Late Proterozoic(?) and Early Cambrian age (Ratcliffe, 1994).
Lithology: mica schist; conglomerate; dolostone (dolomite); quartzite; phyllite
Undifferentiated Granitic Rocks (Ordovician) at surface, covers 0.2 % of this area
Undifferentiated granitic rocks.
Lithology: granite
Ultramafic Rocks (Ordovician) at surface, covers < 0.1 % of this area
Ultramafic Rocks - Dunite, peridotite, and serpentinite
Lithology: dunite; peridotite; serpentinite
Undifferentiated Granitic Gneiss (Devonian) at surface, covers 5 % of this area
Undifferentiated Granitic Gneiss - Small dikes and sills do not show.
Lithology: granitic gneiss
Middlebury and Chazy Limestone, Undifferentiated Youngman and Carman Formations, Day Point Member (Ordovician) at surface, covers < 0.1 % 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
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
Undifferentiated Gneiss (Precambrian) at surface, covers < 0.1 % of this area
Undifferentiated Gneiss - Undifferentiated gneissic biotite granite, quartz monzonite, and granodiorite.
Lithology: granitic gneiss; quartz monzonite; granodiorite
Middlebury and Chazy Limestone, Undifferentiated Youngman and Carman Formations, Valcour Member (Ordovician) at surface, covers < 0.1 % 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
Bascom Formation, and undifferentiated Luke Hill, Naylor Ledge and Hastings Creek Limestones (Ordovician) at surface, covers 1 % 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
Hoosac Formation (Lower Cambrian and Proterozoic Z) at surface, covers < 0.1 % of this area
Hoosac Formation - Rusty, gray, quartz-albite-mica (-chlorite) schist and gneiss. Locally conglomeratic.
Lithology: mica schist; gneiss
Partridge Formation (Ordovician) at surface, covers 0.1 % of this area
Partridge Formation - Rusty weathering carbonaceous mica schist locally containing porphyroblasts of biotite, garnet, or staurolite. (Southeastern Vermont).
Lithology: mica schist
Poultney Formation ("A" Member) (Cambrian) at surface, covers < 0.1 % of this area
Poultney Formation ("A" Member) - shale, limestone; Hatch Hill Formation-shale, dolostone; West Castleton Formation-shale, limestone, conglomerate.
Lithology: shale; limestone; dolostone (dolomite); conglomerate
Missisquoi Formation, Moretown Member (Ordovician) at surface, covers 4 % 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
Dalton Formation (Cambrian) at surface, covers 0.3 % of this area
Dalton Formation - Schistose quartzite containing pebbles of feldspar and blue quartz; impure dolomite containing pebbles of quartz and feldspar occurs locally; conglomerate common near base. Occurs in southwestern Vertmont.
Lithology: quartzite; dolostone (dolomite); conglomerate
Rowe Schist (Lower Ordovician and Cambrian) at surface, covers < 0.1 % of this area
Rowe Schist - Light-green to light-bluish-gray schist having thin granular quartz lenses and lamellae. Kyanite and staurolite typical at higher grades.
Lithology: schist
Hornblende-biotite diorite; gabbro (Permian-Triassic) at surface, covers < 0.1 % of this area
Hornblende-biotite diorite; gabbro.
Lithology: diorite; gabbro
Morses Line Formation (Ordovician) at surface, covers 0.4 % of this area
Morses Line Formation - Calcareous and non-calcareous slate; local lenses of thin-bedded limestone, limestone conglomerate, and dolomite; in St. Albans synclinorium.
Lithology: slate; limestone; conglomerate; dolostone (dolomite)
Rowe Schist (Lower Ordovician and Cambrian) at surface, covers < 0.1 % of this area
Rowe Schist - Fine- to medium-grained, well-layered and foliated amphibolite; epidote-rich layers locally abundant. Includes its typical Chester Amphibolite Member at Chester, Massachusetts.
Lithology: amphibolite
Mettawee Slate (Cambrian?) at surface, covers < 0.1 % of this area
Mettawee Slate (Bull in Vermont) - includes Castleton (North Brittain) Conglomerate. Mudd Pond Quartzite, Zion Hill Quartzite, and Bomoseen Graywacke Members.
Lithology: slate; quartzite; conglomerate; graywacke
Winooski Dolomite (Cambrian) at surface, covers 0.8 % 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)
Stockbridge Formation (Lower Cambrian) at surface, covers < 0.1 % of this area
Stockbridge Formation - Massive to finely laminated steel-gray calcitic dolomite marble containing a prominent zone of white quartz nodules near top.
Lithology: marble
Taconic Melange (Middle Ordovician) at surface, covers < 0.1 % of this area
Taconic Melange - chaotic mixture of Early Cambrian thru Middle Ordovician pebble to block-size clasts in a pelitic matrix of Middle Ordovician (Barneveld) age. Rims and floors earlier submarine gravity slides of Taconian Orogeny.
Lithology: melange
Lower part of Rangeley Formation (Lower Silurian (Llandoverian)) at surface, covers < 0.1 % of this area
Lower part of Rangeley Formation - Gray, thinly laminated (5-25 mm) metapelite with local lentils of turbidites and thin quartz conglomerates in western New Hampshire. Sparse calc-silicate pods and coticule. Probably equivalent to member B of Rangeley Formation of Maine.
Lithology: meta-argillite; meta-conglomerate; calc-silicate rock
Hoosac Formation, Amphibolite and Greenstone (Cambrian) at surface, covers < 0.1 % of this area
Hoosac Formation, Amphibolite and Greenstone - Amphibolite and actinolitic greenstone. (Southern and Central Vermont).
Lithology: amphibolite; greenstone
Pinney Hollow Formation, Ottauquechee, and Stowe Formations, Undifferentiated (Ordovician) at surface, covers 0.2 % of this area
Pinney Hollow Formation, Ottauquechee, and Stowe Formations, Undifferentiated - Includes quartz-muscovite-garnet-chlorite-biotite schist, rusty carbonaceous schist, amphibolite, and schistose quartzite. Schist locally contains porphyroblasts of staurolite and kyanite. On flanks of Chester and Athens domes.
Lithology: mica schist; schist; amphibolite; quartzite
Missisquoi Formation, Cram Hill Member (Ordovician) at surface, covers 0.1 % 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
Orwell Limestone and Isle la Motte and Lowville Limestones (Ordovician) at surface, covers 0.1 % 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
Stockbridge Formation (Lower Cambrian) at surface, covers < 0.1 % of this area
Stockbridge Formation - Beige, tan, and dark-gray weathering quartzose dolomite marble containing interbeds of black, green and maroon phyllite and punky weathering blue quartz pebble quartzite.
Lithology: marble; phyllite; quartzite
Gile Mountain Formation, Meetinghouse Slate Member (Lower Devonian ) at surface, covers < 0.1 % of this area
Meetinghouse Slate Member - Gray to black phyllite and silty metasandstone turbidite.
Lithology: phyllite; metasedimentary rock
Metavolcanic and metasedimentary rocks of the lower part of Ammonoosuc Volcanics, undivided (Middle Ordovician) at surface, covers < 0.1 % of this area
Metavolcanic and metasedimentary rocks of the lower part of Ammonoosuc Volcanics, undivided.
Lithology: metavolcanic rock; metasedimentary rock
Sherman Marble (Proterozoic Y) at surface, covers < 0.1 % of this area
Sherman Marble - White, coarse-grained graphite dolomite-calcite marble at Sherman Reservoir at the State line.
Lithology: marble
Biotite-quartz-plagioclase paragneiss, amphibolite, and related migmatite (Middle Proterozoic) at surface, covers < 0.1 % of this area
Biotite-quartz-plagioclase paragneiss, amphibolite, and related migmatite - locally sillimanitic; commonly garnetiferous in and adjacent to Adirondack Highlands.
Lithology: paragneiss; amphibolite; migmatite
Hoosac Formation (Lower Cambrian and Proterozoic Z) at surface, covers < 0.1 % of this area
Hoosac Formation - Green to gray-green chlorite-sericite-quartz phyllite; interbeds of chloritoid- or albite-rich schist and minor quartzite, locally rich in garnet and kyanite.
Lithology: phyllite; schist; quartzite
Missisquoi Formation, Harlow Bridge Quartzite Member (Ordovician) at surface, covers < 0.1 % of this area
Missisquoi Formation, Harlow Bridge Quartzite Member - Buff to pale-green quartzite with interbeds of quartz-sericite-chlorite phyllite.
Lithology: quartzite; phyllite
Metadiorite (Devonian) at surface, covers < 0.1 % of this area
Metadiorite - Dikes and sills of metagabbro, metadiabase and meta-andesite too small to show are chiefly in the Missisquoi, Albee, and Orfodville formations.
Lithology: metavolcanic rock
Orfordville Formation, Post Pond Volcanics (Ordovician) at surface, covers 0.3 % of this area
Orfordville Formation, Post Pond Volcanics - Greenstone, green chloritic schist interbedded with schistose felsite, quartz-feldspar-sericite schist; fine-grained chloritic, biotitic gneiss, all west of Ammonoosuc fault; mainly amphibolite east of the Ammonoosuc fault.
Lithology: greenstone; greenschist; mica schist; biotite gneiss; amphibolite
Ammonoosuc Volcanics (Ordovician) at surface, covers < 0.1 % of this area
Ammonoosuc Volcanics - Fine-grained chloritic and biotitic gneiss and greenstone in areas north of Bellows Falls; biotite gneiss and amphibolite south of Bellows Falls. (Southeastern Vermont).
Lithology: biotite gneiss; greenstone; amphibolite
Hoosac Formation (Lower Cambrian and Proterozoic Z) at surface, covers < 0.1 % of this area
Hoosac Formation - Greenish chlorite-albite-magnetite-sericite-quartz schist and granofels.
Lithology: mica schist; granofels
Stamford Granite Gneiss (Proterozoic Y) at surface, covers < 0.1 % of this area
Stamford Granite Gneiss - White to gray biotite-oligoclase-microcline Rapakivi granite gneiss containing blue quartz. Intrudes Yb, Ybu.
Lithology: granitic gneiss
Cavendish Formation, Readsboro Member (Cambrian?) at surface, covers 0.9 % of this area
Cavendish Formation, Readsboro Member - Quartz-muscovite schist containing biotite or chlorite and characterized by conspicuous porphyroblasts of sodic plagioclase; less commonly quartz-muscovite-paragonite schist containing chlorite, garnet, or chloritoid, or, in Chester dome, quartz-muscovite-paragonite schist containing garnet, staurolite, and locally kyanite (Gassetts schist). The Cavendish Formation is reinstated and considered part of the Mount Holly Complex in VT. Usage follows Thompson (1950), but is extended to include some rocks on Star Hill, including inner and outer cover rocks assigned by Downie (1982) to Hoosac and Pinney Hollow Formations. Formation is divided into four map units: calc-silicate rock and gneiss, marble, feldspathic schist or granofels, and the Gassetts Schist Member. The Cavendish correlates with the Wilcox Formation of the Mount Holly Complex in the Green Mountain massif, and therefore, is of Middle Proterozoic age (Ratcliffe, in press).
Lithology: mica schist; schist
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
Waits River formation, Standing Pond Volcanic Member (Devonian) at surface, covers 0.5 % 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
Gray, well-layered biotite-plagioclase-quartz gneiss (Proterozoic Y) at surface, covers < 0.1 % of this area
Gray, well-layered biotite-plagioclase-quartz gneiss - Containing beds of amphibolite, aluminous schist, quartzite, and calc-silicate gneiss.
Lithology: granitic gneiss; amphibolite; schist; quartzite; gneiss
Iberville Formation (Ordovician) at surface, covers 0.8 % 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)
Greenvale Cove Formation (Lower Silurian? ) at surface, covers < 0.1 % of this area
Greenvale Cove Formation - Grayish-violet interlaminated metashale, feldspathic metasandstone, and calc-silicate rock of the Piermont allochthon in western New Hampshire.
Lithology: meta-argillite; metasedimentary rock; calc-silicate rock
Sweetsburg Formation, Rockledge Conglomerate Member (Cambrian) at surface, covers < 0.1 % of this area
Sweetsburg Formation, Rockledge Conglomerate Member - Phenoclasts chiefly of biohermal limestone in a matrix of gray limestone containing frosted quartz sand grains.
Lithology: conglomerate; limestone
Ammonoosuc Volcanics, Felsic metavolcanic rocks (Middle - Upper Ordovician) at surface, covers < 0.1 % of this area
Ammonoosuc Volcanics, Felsic metavolcanic rocks.
Lithology: felsic metavolcanic rock
Saxe Brook Dolomite (Cambrian) at surface, covers < 0.1 % of this area
Saxe Brook Dolomite - Sandy gray dolomite, sandstone containing dolomitic cement, and pure dolomite; on west limb of St. Albans synclinorium.
Lithology: dolostone (dolomite); sandstone
Hoosac Formation (Lower Cambrian and Proterozoic Z) at surface, covers < 0.1 % of this area
Hoosac Formation - Undifferentiated Hoosac Formation.
Lithology: schist; phyllite; gneiss; amphibolite; quartzite; granofels; calc-silicate rock
Littleton Formation, undivided (Lower Devonian; Siegenian) at surface, covers < 0.1 % of this area
Littleton Formation undivided - Gray metapelite and metawacke and subordinate metavolcanic rocks; generally, but not everywhere, conformable with underlying Fitch or Madrid Formations. Fossiliferous in western New Hampshire.
Lithology: metasedimentary rock; metavolcanic rock
Stowe Formation, carbonaceous schist and phyllite (Cambrian-Ordovician) at surface, covers 0.1 % 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
Bascom Formation, and undifferentiated Luke Hill, Naylor Ledge and Hastings Creek Limestones; Brownell Mountain Phyllite Member (Ordovician) at surface, covers < 0.1 % of this area
Bascom Formation , and undifferentiated Luke Hill, Naylor Ledge and Hastings Creek Limestones; Brownell Mtn Phyllite Member - Calcareous phyllite in upper part of the Bascom Formation of east limb of Hinesburg synclinorium.
Lithology: phyllite
Syenite (Permian-Triassic) at surface, covers 0.1 % of this area
Syenite - Hornblende, biotite, quartz and augite syenites.
Lithology: syenite; quartz syenite
Cheshire Quartzite (Lower Cambrian) at surface, covers < 0.1 % of this area
Cheshire Quartzite - White, massive vitreous quartzite.
Lithology: quartzite
Bethlehem Granodiorite (Early Devonian) at surface, covers < 0.1 % of this area
Bethlehem Granodiorite (Bethlehem Gneiss of Billings, 1955) - Gray, strongly foliated biotite-muscovite granodiorite and associated tonalite and granite.
Lithology: granodiorite; tonalite; granite
Dunham Dolomite (Cambrian) at surface, covers 2 % 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)
Shelburne, Whitehall, and Strites Pond Formations (Ordovician) at surface, covers 0.7 % 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)
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
Undifferentiated Middle Ordovician thru Lower Cambrian allochthonous rocks (Cambrian - Ordovician) at surface, covers < 0.1 % of this area
Undifferentiated Middle Ordovician thru Lower Cambrian allochthonous rocks - principally pelite; lesser quartzite, limestone, conglomerate, graywacke.
Lithology: mudstone; quartzite; limestone; conglomerate; graywacke
Sweetsburg Formation, St. Albans Slate Member (Cambrian) at surface, covers < 0.1 % of this area
Sweetsburg Formation, St. Albans Slate Member - Black, gray-black, or tan micaceous slate.
Lithology: slate
Clough Formation (Silurian) at surface, covers < 0.1 % of this area
Clough Formation - Quartzite, quartz-conglomerate, and mica schist; lenses of fossiliferous calcareous quartzite in upper part. (Southeastern Vermont).
Lithology: conglomerate; quartzite; mica schist
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
Gile Mountain Formation, Amphibolite (Devonian) at surface, covers < 0.1 % of this area
Gile Mountain Formation, Amphibolite - Hornblende-quartz-biotite-chlorite rock.
Lithology: amphibolite
Hornblende granite to granodiorite (Late Ordovician) at surface, covers < 0.1 % of this area
Hornblende granite to granodiorite - Part of Lost Nation pluton of northwestern New Hampshire.
Lithology: granite; granodiorite
Ammonoosuc Volcanics, Bimodal volcanic rocks (Middle - Upper Ordovician) at surface, covers < 0.1 % of this area
Ammonoosuc Volcanics, Bimodal volcanic rocks - Locally includes unmapped Oals.
Lithology: bimodal suite
Goshen Formation (Lower Devonian) at surface, covers < 0.1 % of this area
Goshen Formation - Well-bedded micaceous quartzite or quartz schist grading upward into light- to dark-gray, carbonaceous aluminous schist in beds 5 to 15 cm thick.
Lithology: schist; quartzite
Fitch Formation (Silurian) at surface, covers < 0.1 % of this area
Fitch Formation - Quartz-plagioclase-biotite granulite; actinolite-diopside granulite; impure limestone and dolomite; mica schist; the carbonate-rich beds are typically an inch or two thick and segmented so as to give the weathered outcrop a characteristic pitted appearance. (Southeastern Vermont).
Lithology: granulite; limestone; dolostone (dolomite); mica schist
Granites (Permian-Triassic) at surface, covers < 0.1 % of this area
Granites - Biotite and hornblende granites.
Lithology: granite
Rangeley Formation, undivided (Lower Silurian (Llandoverian)) at surface, covers < 0.1 % of this area
Rangeley Formation, undivided.
Lithology: metasedimentary rock; calc-silicate rock; meta-argillite; quartzite; pelitic schist; granofels; felsic metavolcanic rock
Northfield Formation (Devonian - Silurian) at surface, covers 0.8 % 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
Orwell Limestone, Isle la Motte and Lowville Limestones; Root Pond quartzite member (Ordovician) at surface, covers < 0.1 % of this area
Orwell Limestone, Isle la Motte and Lowville Limestones; Root Pond quartzite member - Massive quartz sandstone, near Benson and West Haven, that overlies Orwell limestone.
Lithology: sandstone
St. Catherine Formation, Bomoseen Graywacke Member (Cambrian) at surface, covers 0.2 % of this area
St. Catherine Formation, Bomoseen Graywacke Member - Green to olive-colored arkose and graywacke that weathers pale red to white; contains visible flakes of mica and rock fragments.
Lithology: arkose; graywacke
Pinnacle Formation, Tibbit Hill Volcanic Member (Cambrian) at surface, covers 0.5 % of this area
Pinnacle Formation, Tibbit Hill Volcanic Member - Albite-actinolite-chlorite-epidote greenstone; locally pillowed and vesicular. (Northern and Central Vermont).
Lithology: greenstone
Potsdam Sandstone (Cambrian) at surface, covers < 0.1 % of this area
Potsdam Sandstone (Covey Hill in Quebec)
Lithology: sandstone
Danby and Potsdam Formations (Cambrian) at surface, covers 0.4 % 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)
Waits River Formation (Devonian) at surface, covers 15 % 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
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
Clarendon Springs, Ticonderoga, and Rock River Dolomites; Gorge Formation (Cambrian) at surface, covers 0.6 % 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
Parker Slate (Cambrian) at surface, covers < 0.1 % of this area
Parker Slate - Gray to black micaceous shale and slate, includes dolomite, sandstone, and quartzite lenses; chiefly on west limb of St. Albans synclinorium.
Lithology: slate; shale; dolostone (dolomite); sandstone; quartzite
Ammonoosuc Volcanics, Metabasalt (Middle - Upper Ordovician) at surface, covers < 0.1 % of this area
Ammonoosuc Volcanics, Metabasalt.
Lithology: meta-basalt
Underhill Formation, Peaked Mountain Member (Cambrian) at surface, covers < 0.1 % of this area
Underhill Formation, Peaked Mountain Member - Greenstone. (Northern and Central Vermont).
Lithology: greenstone
Mount Holly Complex, quartzite and schist (Precambrian) at surface, covers 1 % 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
Stony Point Formation (Ordovician) at surface, covers 2 % 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)
Gile Mountain Formation, Meetinghouse Slate Member (Devonian) at surface, covers 0.3 % of this area
Gile Mountain Formation, Meetinghouse Slate Member - Chiefly gray slate or phyllite characterized by beds of gray schistose quartzite 1/8 inch to 3 inches thick. Gile Mountain Formation and its Meetinghouse Slate Member were previously considered to be Early Devonian based on Emsian plant fossils from Compton Formation of QUE (Hueber and others, 1990; Hatch, 1991). Age assignment here changed to Early Devonian(?) because recent mapping indicates that Gile Mountain and Compton are not coextensive across VT-QUE border as formerly believed by Doll and others (1961, State map) and St. Julien and Slivitsky (1987). Instead, the formations are separated by Ironbound Mountain Formation. Ironbound Mountain Formation is conformably overlain by Compton, but it is not yet known whether Ironbound Mountain is overlain or underlain by Gile Mountain; this is shown by queried Ironbound Mountain-Gile Mountain contact in area of Averill 7.5-min quad, VT. Correlation of Gile Mountain and Compton is justified only if Gile Mountain in this area conclusively is shown to be underlain by Ironbound Mountain; otherwise, Gile Mountain (with possible exception of its Meetinghouse Slate Member) would be coeval with Silurian Frontenac Formation. Hatch (1988) proposed that Meetinghouse represents upper part of Gile Mountain on basis of graded bedding seen south of map area. This relationship is not proven, however, because Gile Mountain-Meetinghouse contact is difficult to define and graded beds are not always easily interpreted. On this map, Meetinghouse is tentatively shown to occur below main body of Gile Mountain on basis of remarkable similarity between it and Ironbound Mountain Formation. This relationship easily explains highly pelitic character of the Meetinghouse with upward-coarsening character of Lower Devonian sequences elsewhere in map area. Meetinghouse Slate Member includes volcanic facies (Moench and others, 1995).
Lithology: slate; phyllite; quartzite
Hortonville Formation (Ordovician) at surface, covers 0.6 % 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
Waits River Formation (Lower Devonian) at surface, covers < 0.1 % of this area
Waits River Formation - Interbedded medium- to dark-gray, moderately rusty weathering, highly contorted, unbedded schist and punky-weathering calcareous granofels or quartzose marble, and pods and stringers of vein quartz.
Lithology: schist; granofels; marble
Ottauquechee Formation (Cambrian) at surface, covers 1 % 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
Moosalamoo Phyllite (Cambrian) at surface, covers < 0.1 % of this area
Moosalamoo Phyllite - Gray to black sericite-quartz phyllite; sericite-quartz-chlorite phyllite occurs locally.
Lithology: phyllite
Chipman, Bridport, and Beldens Formations, Providence Island Dolomite; Burchards Member (Ordovician) at surface, covers < 0.1 % 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)
Cheshire Quartzite (Cambrian) at surface, covers 2 % 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
Pinney Hollow Formation (Cambrian) at surface, covers 2 % 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
Nassau Formation (Lower Cambrian and Proterozoic Z) at surface, covers < 0.1 % of this area
Nassau Formation - Lustrous, soft green, yellowish-green and purple laminated chloritoid-chlorite phyllite (Mettawee Member).
Lithology: phyllite
Hawley Formation (Middle Ordovician) at surface, covers < 0.1 % of this area
Hawley Formation - Black, fine-grained, splintery, rusty-weathering schist and thin dark quartzite; interlayered amphibolite commonly has plagioclase megacrysts. As used here the Hawley includes amphibolite, sulfidic rusty schists, abundant coticules, silvery schists, quartzites and quartz conglomerates, and quartz, feldspar, biotite granulites. The quartzites and quartz conglomerates occur at two positions in rocks here assigned to the Hawley. Those occurring near the top have been mapped previously as Russell Mountain Formation or as Shaw Mountain Formation. The Hawley overlies the Ordovician Barnard Gneiss and underlies Silurian and Devonian "calciferous schists" that include the westernmost Goshen Formation in MA and Northfield Formation in southern VT, the central Waits River Formation and the eastern Gile Mountain Formation. Authors believe that the Goshen, Northfield, and Waits River are facies equivalents, while the Gile Mountain is slightly younger. Map symbol indicates that Hawley is Ordovician and Silurian. 40Ar/3Ar hornblende release spectrum date of 433+/-3 Ma obtained by Spear and Harrison (1989) (Trzcienski and others, 1992).
Lithology: schist; quartzite; amphibolite
Frontenac Formation, Mixed volcanic and sedimentary facies (Silurian?) at surface, covers < 0.1 % of this area
Frontenac Formation, Mixed volcanic and sedimentary facies.
Lithology: metavolcanic rock; metasedimentary rock
Stowe Formation, greenstone and amphibolite (Cambrian-Ordovician) at surface, covers 0.6 % of this area
Stowe Formation, greenstone and amphibolite - Epidote-albite-chlorite rocks contain actinolite and hornblende where more metamorphosed.
Lithology: greenstone; amphibolite
Brezee Formation, quartzose green phyllite (Cambrian) at surface, covers < 0.1 % of this area
Brezee Formation, quartzose green phyllite.
Lithology: phyllite
Monkton Quartzite (Cambrian) at surface, covers 0.9 % 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)
Tonalite (Middle Ordovician) at surface, covers < 0.1 % of this area
Tonalite - Extended from Joslin Turn, Vermont.
Lithology: tonalite
Waits River Formation, Crow Hill Member (Devonian) at surface, covers < 0.1 % of this area
Waits River Formation, Crow Hill Member - Tough gray quartzite near St. Johnsbury is distinctive; similar rock (not shown on map) occurs at several other places.
Lithology: quartzite
Orfordville Formation (Ordovician) at surface, covers 0.1 % of this area
Orfordville Formation - Carbonaceous phyllite; minor quartzite.
Lithology: phyllite; quartzite
Smalls Falls Formation, undivided (Upper to Middle Silurian (Ludlovian and Wenlockian)) at surface, covers < 0.1 % of this area
Smalls Falls Formation, undivided -Very rusty weathering, thinly bedded sulfidic-graphitic schist and pyrrhotitic calc-silicate granofels. Eastern facies equivalent to lower part of the Fitch Formation. Locally mapped as Francestown Formation of Nielson (1981) in southern New Hampshire.
Lithology: schist; granofels
Rugg Brook Formation (Cambrian) at surface, covers 0.1 % of this area
Rugg Brook Formation - Sandy gray dolomite, dolomite conglomerate, and interbeds of gray-weathered sandstone, in St. Albans and Middlebury synclinoria.
Lithology: dolostone (dolomite); conglomerate; sandstone
Stamford Gneiss (Precambrian) at surface, covers 0.1 % of this area
Stamford Gneiss - Granitic biotite gneiss with megacrysts of microcline. A dike-like feature of Stamford Granite, found near eastern margin of Green Mountain massif near locality 1 on this map (represented by sample 172), was incorrectly referred to as a probable Late Proterozoic diabase dike by Ratcliffe on his section of the Bedrock Map of Massachusetts (Zen and others, 1983). U-Pb zircon dates from Karabinos and Aleinikoff (1988, 1990) yield an age of 959+/-4 Ma. Unpublished data from Harding and Mukasa yield a U-Pb zircon date of about 950 Ma (Ratcliffe and others, 1993).
Lithology: biotite gneiss
Underhill Formation, Foot Brook Member (Cambrian) at surface, covers 0.1 % of this area
Underhill Formation, Foot Brook Member - Sericite (muscovite-paragonite)-quartz-chlorite-chloritoid schist; minor carbonaceous interbeds. (Northern and Central Vermont).
Lithology: mica 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
St. Catherine Formation (Cambrian) at surface, covers 3 % 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
Chipman, Bridport, and Beldens Formations, Providence Island Dolomite; Beldens Member (Ordovician) at surface, covers 0.4 % 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
Partridge Formation, Volcanics (Ordovician) at surface, covers < 0.1 % of this area
Partridge Formation, Volcanics - fine-grained biotite gneiss and amphibolite. (Southeastern Vermont).
Lithology: biotite gneiss; amphibolite
Pinney Hollow Formation, carbonaceous phyllite and schist (Cambrian) at surface, covers 4 % of this area
Pinney Hollow Formation, carbonaceous phyllite and schist. (Southern and Central Vermont).
Lithology: phyllite; schist
Smalls Falls Formation, Mixed metavolcanic rocks and metavolcanic sediments (Upper to Middle Silurian (Ludlovian and Wenlockian)) at surface, covers < 0.1 % of this area
Smalls Falls Formation, Mixed metavolcanic rocks and metavolcanic sediments.
Lithology: metavolcanic rock
Ultramafic Rocks (Ordovician) at surface, covers < 0.1 % of this area
Ultramafic Rocks - Undifferentiated ultramafic rocks.
Lithology: ultramafic intrusive rock
Ironbound Mountain Formation, undivided (Lower Devonian) at surface, covers < 0.1 % of this area
Ironbound Mountain Formation, undivided - Interbedded gray phyllite, in places containing feldspathic clasts, and feldspathic metasandstone, variably graded.
Lithology: phyllite; metasedimentary rock
Gile Mountain Formation, undivided (Lower Devonian) at surface, covers < 0.1 % of this area
Gile Mountain Formation, undivided - Gray to tan metawacke and schist or phyllite; gradational into Meetinghouse Slate Member but more thickly bedded and less pelitic than the member. Includes minor metavolcanic lentils.
Lithology: schist; metasedimentary rock; phyllite; slate; metavolcanic rock
Frontenac Formation, undivided (Silurian?) at surface, covers < 0.1 % of this area
Frontenac Formation, undivided - Interbedded thick feldspathic wackes, tan and green slates, and minor calcareous lenses.
Lithology: metasedimentary rock; slate
Sweetsburg Formation, Hungerford Slate Member (Cambrian) at surface, covers < 0.1 % of this area
Sweetsburg Formation, Hungerford Slate Member - Black slate.
Lithology: slate
Missisquoi Formation, Coburn Hill Volcanic Member (Ordovician) at surface, covers < 0.1 % 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
Gile Mountain Formation, Hall Stream Member (Devonian) at surface, covers < 0.1 % of this area
Gile Mountain Formation, Hall Stream Member - Highly feldspathic grit, probably volcanic; feldspathic chlorite-ankerite schist and amphibolite; all northeast of Nulhegan River.
Lithology: schist; amphibolite
Littleton Formation (Devonian) at surface, covers 0.5 % of this area
Littleton Formation - Gray slate and phyllite containing interbeds of gray schistose quartzite 1/4 inch to 6 inches thick. West of Guildhall are lustrous, light to dark gray biotite-garnet phyllite and schist, some slate, and subordinate quartzite and impure quartzite. South of Bellows Falls gray phyllite passes eastward into gray mica schist containing porphyroblasts of biotite, garnet, and staurolite.
Lithology: slate; phyllite; quartzite; schist; mica schist
Mount Holly Complex (Precambrian) at surface, covers 7 % 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
Dalton Formation (Lower Cambrian and Proterozoic Z) at surface, covers < 0.1 % of this area
Dalton Formation - Tan to orangish-tan quartz and gneiss cobble and pebble conglomerate, rusty feldspathic schist, and lustrous greenish-gray muscovite quartz schist.
Lithology: conglomerate; schist; mica schist
Brezee Formation (Cambrian) at surface, covers 0.6 % of this area
Brezee Formation - Dark gray to black phyllite with beds of blue-gray marble, dark gray dolomite, sandy dolomite, and dolomitic sandstone, in upper part; beds of massive quartzite as much as 20 ft thick occur locally and in places contain pebbles of blue quartz. Phyllites are locally highly albitic.
Lithology: phyllite; marble; dolostone (dolomite); sandstone; quartzite
Waits River Formation (Lower Devonian) at surface, covers < 0.1 % of this area
Waits River Formation - Amphibolite or hornblende schist locally containing conspicuous hornblende or garnet megacrysts. Rocks mapped as Conway Schist by Emerson (1898, 1917) and subsequently subdivided by Segerstrom (1956) and Willard (1956) were mapped across the MA-VT State line as Waits River and Gile Mountain Formations by Doll and others (1961) on Centennial Geologic Map of Vermont. Although controversy still exists over relative ages, detailed reconnaissance mapping by authors and S.F. Clark, Jr., L.M. Hall, and J.W. Pferd shows that Waits River and Gile Mountain Formations are readily distinguished in the field. For these reasons, and to maintain continuity across the State line, authors chose to follow VT nomenclature on here and on MA State bedrock geologic map (Zen and others, 1983). Primary difference between Waits River and Gile Mountain is presence in Gile Mountain of beds of noncalcareous, commonly micaceous quartzite. Both formations contain conspicuous beds of punky brown-weathering impure marble or calcareous granulite, mostly in Waits River and less abundant in Gile Mountain. Predominant lithology of both formations is typically contorted gray, graphitic, locally very sulfidic, moderately aluminous mica schist containing quartz veins. Gradational but definitely significant boundary can be mapped between both formations. Amphibolite in both formations may correlate with Standing Pond Volcanics occurring at or near Waits River-Gile Mountain contact in VT. Report goes into great detail regarding informal subdivision of each formation. Rocks previously mapped as Waits River Formation northeast of Shelburne Falls dome by Hatch and Hartshorn (1968) are here reassigned to an unnamed member of Goshen Formation because the rocks are indistinguishable from the Goshen. Goshen-Waits River contact is defined as the line along which, going eastward, the schist changes from aluminous, planar-bedded, and virtually quartz-free (Goshen), to alumina-poor, contorted, and rich in quartz veins (Waits River) (Hatch and others, 1988).
Lithology: amphibolite; amphibole schist
Moretown Formation (Middle Ordovician or older) at surface, covers < 0.1 % of this area
Moretown Formation - Light-greenish-gray to buff, fine-grained, pinstriped granofels and schist.
Lithology: granofels; schist
Glens Falls Formation, Larrabee Member (Ordovician) at surface, covers < 0.1 % of this area
Glens Falls Formation, Larrabee Member - Thin-bedded shaly limestone. (Glens Falls Formation: Thin bedded, dark blue-gray, rather coarsely granular and highly fossiliferous limestone.)
Lithology: limestone; shale
Walloomsac Formation (Middle Ordovician) at surface, covers < 0.1 % of this area
Walloomsac Formation - slate, phyllite, schist, metagraywacke.
Lithology: slate; phyllite; schist; metasedimentary rock
Middlebury and Chazy Limestone; Undifferentiated Youngman and Carman Formations (Ordovician) at surface, covers 0.4 % 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
Mount Merino and Indian River Formations (Ordovician) at surface, covers < 0.1 % of this area
Mount Merino and Indian River Formations - shale, slate, cherts.
Lithology: shale; slate; chert
Waits River Formation, Barton River Member (Devonian) at surface, covers < 0.1 % 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
Hoosac Formation, Turkey Mountain Member (Cambrian) at surface, covers < 0.1 % of this area
Hoosac Formation, Turkey Mountain Member - Amphibolite and actinolitic greenstone characterized by oval, 1/8 to 3/8 inch spots, chiefly of epidote. (Southern and Central Vermont). Discontinuous lenses of metabasalt, informally referred to as Turkey Mountain metabasalt member of Hoosac Formation, actually occur at different stratigraphic positions extending through a stratigraphic distance of 100 to 400 m above base of Hoosac Formation. From type area on Turkey Mountain in Saxtons River quad south to Massachusetts State line, basalts form at least three relatively persistent units (Ratcliffe, 1991). Basalt mapped in northeast corner of this map, above Wilmington thrust system, correlates with type Turkey Mountain. As used here, Turkey Mountain metabasalt member consists of several laterally and vertically discontinuous, nonidentical flows and volcaniclastic deposits including, but not restricted to, type Turkey Mountain Member of Hoosac Formation as used by Doll and others (1961) and by Skehan (1961). They mapped the lower basalts as unnamed greenstones in Hoosac Formation. Turkey Mountain metabasalt member consists of light-green to dark-green epidote-amphibole greenstones and amphibolite metabasalts. Metabasalt varies from massive to very well layered. Finely laminated, quartzose and epidotitic volcaniclastic beds several centimeters thick are interlayered with more massive, strongly foliated, black amphibolite. Where in contact with surrounding metasedimentary rocks, layering within metabasalt and volcaniclastic beds is concordant and gradational with enclosing metasediment. Light-gray or yellowish-greenish-gray, well-laminated quartzite or, less commonly, gritty, pebbly conglomerate 0.5 to 5 m thick marks upper contact with unnamed granofels member of Hoosac Formation. Base of Turkey Mountain metabasalt member in contact with rusty muscovite-albite-biotite schist. Metabasalts probably originated as thin composite basalt lava flows that contained intercalated basaltic volcaniclastic rocks. Age is Late Proterozoic and Early Cambrian (Ratcliffe, 1993).
Lithology: amphibolite; greenstone
Hazens Notch Formation, sericite-quartz-chlorite-albite-magnetite schist (Cambrian) at surface, covers 0.1 % of this area
Hazens Notch Formation, sericite-quartz-chlorite-albite-magnetite schist - near Hyde Park. (Northern and Central Vermont).
Lithology: mica schist
Nepheline Syenite and Pulaskite (Permian-Triassic) at surface, covers < 0.1 % of this area
Nepheline Syenite and Pulaskite.
Lithology: nepheline syenite
Hawley Formation (Middle Ordovician) at surface, covers < 0.1 % of this area
Hawley Formation - Interbedded amphibolite, greenstone, feldspathic schist and granofels. Coarse plagioclase in some amphibolite near top; local coarse hornblende blades or sprays. Sparse coticule (Emerson, 1917, p. 43). As used here the Hawley includes amphibolite, sulfidic rusty schists, abundant coticules, silvery schists, quartzites and quartz conglomerates, and quartz, feldspar, biotite granulites. The quartzites and quartz conglomerates occur at two positions in rocks here assigned to the Hawley. Those occurring near the top have been mapped previously as Russell Mountain Formation or as Shaw Mountain Formation. The Hawley overlies the Ordovician Barnard Gneiss and underlies Silurian and Devonian "calciferous schists" that include the westernmost Goshen Formation in MA and Northfield Formation in southern VT, the central Waits River Formation and the eastern Gile Mountain Formation. Authors believe that the Goshen, Northfield, and Waits River are facies equivalents, while the Gile Mountain is slightly younger. Map symbol indicates that Hawley is Ordovician and Silurian. 40Ar/3Ar hornblende release spectrum date of 433+/-3 Ma obtained by Spear and Harrison (1989) (Trzcienski and others, 1992).
Lithology: amphibolite; greenstone; schist; granofels
Hoosac Formation, Plymouth Member (Cambrian) at surface, covers 0.1 % of this area
Hoosac Formation, Plymouth Member - Quartzite, schistose quartzite, dolomitic quartzite; carbonaceous phyllite; buff to dark gray dolomite with partings locally of carbonaceous phyllite; quartz-sericite-chlorite-albite schist; carbonaceous albite schist. (Southern and Central Vermont). Revised the Plymouth Member of the Hoosac Formation of Doll and others (1961) to the Plymouth Formation. Consists of a series of feldspathic and dolomitic quartzites, dolostones and black phyllites that overlie probable Middle Proterozoic gneisses. The Plymouth Formation can be divided into several informal members. The lower contact of the formation is below a sequence of dolomitic quartzites or thin bedded quartzite. Dark laminated silty phyllites laterally replace the more feldspathic quartzites and dark-gray schistose quartzites, massive vitreous quartzites, and dolomitic quartzites pass upward to the east into well bedded cream-weathered light-gray dolostone breccia; these lithologies make up the dolostone member of the Plymouth Formation. The upper member of the Plymouth Formation is a black graphitic and siliceous phyllite that contains 1 to 3 cm thick layers of dark-gray ferruginous quartzite, dolomitic quartzite, and ribbony beds of dolostone. The upper contact of the Plymouth Formation is placed at the first occurrence of light-silvery-green magnetite-muscovite-quartz knotted phyllites of the Pinney Hollow Formation (Ratcliffe, 1994).
Lithology: quartzite; dolostone (dolomite); phyllite; schist
Bridgeman Hill Formation (Cambrian) at surface, covers < 0.1 % of this area
Bridgeman Hill Formation - Undifferentiated dolomite, slate, and conglomerate, on east limb of St. Albans synclinorium, about equivalent to Dunham, Parker, Rugg Brook, and Saxe Brook Formations.
Lithology: dolostone (dolomite); slate; conglomerate
Hybrid rock: mangeritic to charnockitic gneiss (Middle Proterozoic) at surface, covers < 0.1 % of this area
Hybrid rock: mangeritic to charnockitic gneiss - with xenocrysts of calcic andesine and, locally, xenoliths of anorthosite; with increasing percentage of anorthosite component, passes gradationally into anorthositic rocks.
Lithology: gneiss; anorthosite
Sweetsburg Formation (Cambrian) at surface, covers < 0.1 % of this area
Sweetsburg Formation - Black, carbonaceous, well-cleaved slate with characteristic thin (1-5 mm) whitish silty bedding laminae; in St Albans and Hinesburg synclinoria and Cambridge syncline.
Lithology: slate
Orfordville Formation, Sunday Mountain Volcanics (Ordovician) at surface, covers < 0.1 % of this area
Orfordville Formation, Sunday Mountain Volcanics - Greenstone, chloritic schist, felsite, and quartz-feldspar-sericite schist.
Lithology: greenstone; greenschist; mica schist
Biotite Quartz Diorite Gneiss (Devonian) at surface, covers < 0.1 % of this area
Biotite quartz diorite gneiss.
Lithology: granitic gneiss
Cumberland Head Formation (Ordovician) at surface, covers < 0.1 % of this area
Cumberland Head Formation - Interbedded calcareous black shale and fine-grained homogenous, dark-gray limestone; shown only in Grand Isle County where it is thick enough and well enough exposed to map.
Lithology: black shale; limestone
Walloomsac Formation (Middle Ordovician) at surface, covers < 0.1 % of this area
Walloomsac Formation - Dark-gray, graphitic quartz phyllite and schist containing minor lenses of limestone.
Lithology: phyllite; schist; limestone
Hatch Hill and West Castleton Formations, Undifferentiated (Cambrian) at surface, covers 0.2 % 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
Littleton Formation (Lower Devonian) at surface, covers < 0.1 % of this area
Littleton Formation - Black to gray aluminous mica schist, quartzose schist, and aluminous phyllite.
Lithology: schist; phyllite
Missisquoi Formation, Umbrella Hill Member (Ordovician) at surface, covers < 0.1 % 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
Highgate Formation (Ordovician) at surface, covers < 0.1 % of this area
Highgate Formation - Banded blue limestone and calcareous slate; local lenses of limestone conglomerate; on west limb of St. Albans synclinorium.
Lithology: limestone; slate; conglomerate
Littleton Formation, Volcanic lentils (Lower Devonian) at surface, covers < 0.1 % of this area
Littleton Formation, Volcanic lentils - Both mafic and felsic
Lithology: mafic metavolcanic rock; felsic metavolcanic rock
Hazens Notch Formation, Belvidere Mountain Amphibolite Member (Cambrian) at surface, covers < 0.1 % 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
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
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
Fitch Formation (Upper Silurian; Pridolian and Ludlovian) (Upper Silurian - (Pridolian and Ludlovian)) at surface, covers < 0.1 % of this area
Fitch Formation - Metamorphosed limestone, calcareous sandstone, siltstone, and dark pelitic schist; lower contact is disconformable on the Clough Quartzite. Fossiliferous.
Lithology: marble; quartzite; phyllite; pelitic schist
Dalton Formation (Lower Cambrian and Proterozoic Z) at surface, covers < 0.1 % of this area
Dalton Formation - Orangish-gray, gray, and light-greenish-gray muscovite-quartz schist and interlayered feldspathic quartzite and quartz conglomerate; minor beds of rusty albitic schist.
Lithology: mica schist; quartzite; conglomerate; schist
Beekmantown Group (in part) (Lower Ordovician) at surface, covers < 0.1 % of this area
Beekmantown Group (in part) - In St. Lawrence Valley: Ogdensburg Dolostone (Beauharnois Dolostone in Canada); In Champlain Valley: Providence Island Dolostone; Fort Cassin Formation-limestone, dolostone; Fort Ann Formation (Spellman of Clinton and Essex Counties)-limestone, dolostone; Cutting Formation-dolostone (locally cherty), limestone, siltstone. In Vermont: includes Bridport, Bascom, Cutting, and Shelburne carbonates.
Lithology: dolostone (dolomite); limestone; chert; siltstone
Stockbridge Formation (Lower Cambrian) at surface, covers < 0.1 % of this area
Stockbridge Formation - White to light-powdery-blue-gray dolostone with disseminated grains of quartz and prominent sprays of tremolite in higher-grade areas.
Lithology: dolostone (dolomite)
Bethlehem Gneiss (Devonian) at surface, covers < 0.1 % of this area
Bethlehem Gneiss - Two-mica granodiorite gneiss. Revised as the Bethlehem Granodiorite to emphasize its average granodiorite composition. Mapped as the Haverhill, Mount Clough, Indian Pond, and Fairlee plutons. Consists of strongly metamorphosed, foliated, gray, medium-grained biotite granodiorite and local tonalite and granite. Age is Devonian based on isotopic age of 410+/-5 Ma (J.N. Aleinikoff, this report, from Fairlee pluton), which is also consistent with age of 409+/-5 Ma reported by Kohn and others (1992) from Indian Pond pluton and Bellows Falls pluton (the latter is outside of map area in southwestern NH) (Moench and others, 1995).
Lithology: granitic gneiss
Stockbridge Formation (Cambrian - Lower Ordovician) at surface, covers < 0.1 % of this area
Stockbridge Formation - calcitic and dolomitic marble.
Lithology: marble
Underhill Formation, Jay Peak Member (Cambrian) at surface, covers < 0.1 % 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
Hawley Formation (Middle Ordovician) at surface, covers < 0.1 % of this area
Hawley Formation - Pale-buff, light-green or white, medium-grained plagioclase gneiss. As used here the Hawley includes amphibolite, sulfidic rusty schists, abundant coticules, silvery schists, quartzites and quartz conglomerates, and quartz, feldspar, biotite granulites. The quartzites and quartz conglomerates occur at two positions in rocks here assigned to the Hawley. Those occurring near the top have been mapped previously as Russell Mountain Formation or as Shaw Mountain Formation. The Hawley overlies the Ordovician Barnard Gneiss and underlies Silurian and Devonian "calciferous schists" that include the westernmost Goshen Formation in MA and Northfield Formation in southern VT, the central Waits River Formation and the eastern Gile Mountain Formation. Authors believe that the Goshen, Northfield, and Waits River are facies equivalents, while the Gile Mountain is slightly younger. Map symbol indicates that Hawley is Ordovician and Silurian. 40Ar/3Ar hornblende release spectrum date of 433+/-3 Ma obtained by Spear and Harrison (1989) (Trzcienski and others, 1992).
Lithology: gneiss
Gile Mountain Formation (Lower Devonian) at surface, covers < 0.1 % of this area
Gile Mountain Formation - Gray, slightly rusty, poorly bedded phyllite and schist containing 20 cm to 2 m beds of light-gray, fine-grained quartzite, local punky-brown weathering calcareous granofels or quartzose marble, and pods and stringers of vein quartz.
Lithology: phyllite; schist; quartzite; granofels; marble
Stockbridge Formation (Lower Ordovician) at surface, covers < 0.1 % of this area
Stockbridge Formation - White to blue-gray and white layered calcite marble.
Lithology: marble
Moretown Formation (Middle Ordovician or older) at surface, covers < 0.1 % of this area
Moretown Formation - Buff to gray, medium- to coarse-grained, poorly bedded mica-rich schist showing dark-green chlorite clots. Some pinstriped granofels.
Lithology: mica schist; granofels
Poultney Formation ("B" and "C" Members) (Ordovician) at surface, covers < 0.1 % of this area
Poultney Formation ("B" and "C" Members) - shale, slate, siltstone.
Lithology: shale; slate; siltstone
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
Pawlet Formation (Ordovician) at surface, covers 0.2 % of this area
Pawlet Formation - Silver gray to jet black, locally carbonaceous and pyritiferous, micaceous silty slate; interbedded, at intervals of a few inches to tens of feet, by beds of dark gray rusty weathered graywacke a few inches to 6 feet thick. The graywacke contains subangular grains of quartz, and less abundant feldspar and slate fragments, in a gray argillaceous matrix that is locally calcareous.
Lithology: slate; graywacke
Bostonite (Permian-Triassic) at surface, covers < 0.1 % of this area
Bostonite - Many small leucophyres and lamprophyres do not show.
Lithology: trachyte; lamprophyre
Mount Hamilton Formation (Ordovician) at surface, covers 0.3 % 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
Gile Mountain Formation, Mafic metavolcanic member (Lower Devonian ) at surface, covers < 0.1 % of this area
Mafic metavolcanic member - Possibly equivalent to Putney Volcanics of southeastern Vermont.
Lithology: mafic metavolcanic rock
Perry Mountain Formation, Sedimentary and subordinate distal felsic and mafic volcanic facies in Piermont allochthon (Lower?- Middle? Silurian) at surface, covers < 0.1 % of this area
Perry Mountain Formation, Sedimentary and subordinate distal felsic and mafic volcanic facies in Piermont allochthon.
Lithology: metasedimentary rock; felsic metavolcanic rock; mafic metavolcanic rock
St. Catherine Formation, Zion Hill Quartzite Member (Cambrian) at surface, covers < 0.1 % of this area
St. Catherine Formation, Zion Hill Quartzite Member - White weathered green, vitreous chloritic quartzite and graywacke spotted with limonite.
Lithology: quartzite; graywacke
Clough Quartzite (Lower Silurian (upper Llandoverian)) at surface, covers < 0.1 % of this area
Clough Quartzite - Orthoquartzite, quartz metaconglomerate, muscovite schist, minor polymictic metaconglomerate. Disconformable below Fitch Formation and unconformable on Ordovician formations. Equivalent, in part, to member C of Rangeley Formation of Maine. Fossiliferous.
Lithology: quartzite; meta-conglomerate; mica schist
Glens Falls and Orwell Limestones, Undifferentiated (Ordovician) at surface, covers 0.1 % 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
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
Tonalite, diorite, granodiorite, and granite (Late Ordovician ) at surface, covers < 0.1 % of this area
Tonalite, diorite, granodiorite, and granite - More mafic rocks have hornblende; part of Lost Nation pluton.
Lithology: tonalite; diorite; granodiorite; granite
Pink equigranular biotite granite (Late Devonian) at surface, covers < 0.1 % of this area
Pink equigranular biotite granite - Found in Woodsville and Whitefield quadrangles and in small intrusive units in northern and southeastern New Hampshire.
Lithology: granite
Goshen Formation (Lower Devonian) at surface, covers < 0.1 % of this area
Goshen Formation - Dg containing beds of punky-weathering calcareous granofels more than 15 cm thick near the contact with the Waits River Formation.
Lithology: schist; quartzite; granofels
Gile Mountain Formation, Interbedded gray slate or phyllite and brown-weathering calcite-ankerite metasiltstone (Lower Devonian) at surface, covers < 0.1 % of this area
Interbedded gray slate or phyllite and brown-weathering calcite-ankerite metasiltstone - Contains minor marble and quartzite. Resembles Waits River Formation in Vermont.
Lithology: slate; phyllite; metasedimentary rock; marble; quartzite
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
Albee Formation (Ordovician) at surface, covers 2 % of this area
Albee Formation - Massive, gray, white-weathered quartzite and feldspathic quartzite interbedded with greenish-gray slate, phyllite, feldspthic phyllite and quartzose argillaceous phyllite. Micaceous quartzite, quartz-mica schist, mica schist and hornfels contining porphyroblasts of biotite, garnet, staurolite and sillimanite in the vicinity of granitic plutons. Soda-rhyolite tuff occurs locally. Micaceous quartzite characterized by thin, schistose "pinstripe" partings is common in many areas.
Lithology: quartzite; slate; phyllite; mica schist; hornfels; tuff
Dalton Formation (Lower Cambrian and Proterozoic Z) at surface, covers < 0.1 % of this area
Dalton Formation - Tan weathering, muscovite-microcline quartzite and feldspathic quartzite rich in black tourmaline, locally includes thin beds of other rock types listed below.
Lithology: quartzite
Ironbound Mountain Formation, Grits at Halls Stream in northern New Hampshire (Lower Devonian) at surface, covers < 0.1 % of this area
Ironbound Mountain Formation, Grits at Halls Stream in northern New Hampshire - Thickly bedded feldspathic volcaniclastic grit and interbedded gray slate. Equivalent to Grenier Ponds Member of the Ironbound Mountain Formation in western Maine.
Lithology: metavolcanic rock; slate
Chipman, Bridport, and Beldens Formations, Providence Island Dolomite; Weybridge Member (Ordovician) at surface, covers 0.1 % 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
Austerlitz Phyllite (Cambrian?) at surface, covers < 0.1 % of this area
Austerlitz Phyllite - minor quartzite
Lithology: phyllite; quartzite
Missisquoi Formation, Whetstone Hill Member (Ordovician) at surface, covers 0.3 % of this area
Missisquoi Formation, Whetstone Hill Member - Carbonaceous black to light gray phyllite and schist containing porphyroblasts of biotite and garnet; beds of gray micaceous quartzite, fine-grained biotite gneiss and amphibolite.
Lithology: phyllite; schist; quartzite; biotite gneiss; amphibolite
Frontenac Formation, Graded-bedded metagraywacke and subordinate gray phyllite (Silurian?) at surface, covers < 0.1 % of this area
Frontenac Formation, Graded-bedded metagraywacke and subordinate gray phyllite.
Lithology: metasedimentary rock; phyllite
Glens Falls Formation, Shoreham Member (Ordovician) at surface, covers < 0.1 % of this area
Glens Falls Formation, Shoreham Member - Interbedded limestone and shale, contains Cryptolithus tesselatus and Prasopora orientalis. (Glens Falls Formation: Thin bedded, dark blue-gray, rather coarsely granular and highly fossiliferous limestone.)
Lithology: limestone; shale
Metagabbro (Middle Proterozoic) at surface, covers < 0.1 % of this area
Metagabbro - metagabbro, olivine metagabbro, derived amphibolite.
Lithology: mafic metavolcanic rock; amphibolite
Metamorphosed gabbro, diorite, and intrusive basalt dikes (Devonian? - Silurian?) at surface, covers < 0.1 % of this area
Metamorphosed gabbro, diorite, and intrusive basalt dikes - Chiefly in northern New Hampshire.
Lithology: metavolcanic rock
Quartzite, quartz-biotite schist and graphitic schist (Middle Proterozoic) at surface, covers < 0.1 % of this area
Quartzite, quartz-biotite schist and graphitic schist - in part feldspathic, micaceous, garnetiferous, sillimanitic.
Lithology: quartzite; schist

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