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

Geologic units in Grand Isle county, Vermont

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)

Hathaway Formation (Ordovician) at surface, covers 0.4 % 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

Middlebury and Chazy Limestone, Undifferentiated Youngman and Carman Formations, Valcour Member (Ordovician) at surface, covers 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

Iberville Formation (Ordovician) at surface, covers 3 % 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)

Orwell Limestone and Isle la Motte and Lowville Limestones (Ordovician) at surface, covers 0.4 % 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

Middlebury and Chazy Limestone, Undifferentiated Youngman and Carman Formations, Day Point Member (Ordovician) at surface, covers 0.9 % 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

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

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

Lithology: limestone

Glens Falls Formation, Larrabee Member (Ordovician) at surface, covers 2 % 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

Cumberland Head Formation (Ordovician) at surface, covers 2 % 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

Bascom Formation, and undifferentiated Luke Hill, Naylor Ledge and Hastings Creek Limestones (Ordovician) at surface, covers 0.2 % 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

Stony Point Formation (Ordovician) at surface, covers 30 % 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)

Glens Falls Formation, Shoreham Member (Ordovician) at surface, covers 2 % 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