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Geologic units in Somerset county, Pennsylvania

Mauch Chunk Formation (Mississippian) at surface, covers 5 % of this area
Mauch Chunk Formation - Grayish-red shale, siltstone, sandstone, and some conglomerate; some local nonred zones. Includes Loyalhanna Member (crossbedded, sandy limestone) at base in south-central and southwestern Pennsylvania; also includes Greenbrier Limestone Member, and Wymps Gap and Deer Valley Limestones, which are tongues of the Greenbrier. Along Allegheny Front from Blair County to Sullivan County, Loyalhanna Member is greenish-gray, calcareous, crossbedded sandstone.
Lithology: shale; siltstone; sandstone; conglomerate; limestone
Foreknobs Formation (Devonian) at surface, covers 6 % of this area
Foreknobs Formation - Interbedded sandstone, siltstone, and shale; gray to olive gray, red near top; substantial brownish-gray sandstone; some marine fossils; a few conglomerate beds at base and top.
Lithology: sandstone; siltstone; shale; conglomerate
Pocono Group, including the Purslane Sandstone and Rockwell Formation (Mississippian) at surface, covers < 0.1 % of this area
Pocono Group - Gray, white, tan, and brown, thin- to thick-bedded, cross-bedded sandstone, locally conglomeratic; interbedded gray and reddish-brown shale, mudstone, and siltstone; fragmentary plant fossils. Undifferentiated in Garrett and western Allegeny Counties. Includes Purslane Sandstone - White, thick-bedded, coarse-grained sandstone and conglomerate with thin coal beds and red shales. Eastern Allegany and Washington Counties. And also inlcudes Rockwell Formation - Coarse-grained arkosic sandstone, fine-grained conglomerate, and buff shale; dark shale with thin coal beds near base. Eastern Allegany and Washington Counties.
Lithology: sandstone; shale; mudstone; siltstone; conglomerate; coal
Casselman Formation (Pennsylvanian) at surface, covers 13 % of this area
Casselman Formation - Cyclic sequences of shale, siltstone, sandstone, red beds, thin, impure limestone, and thin, nonpersistent coal; red beds are associated with landslides; base is at top of Ames limestone.
Lithology: shale; siltstone; sandstone; clastic; limestone; coal
Allegheny Formation and Pottsville Formation (Pennsylvanian) at surface, covers < 0.1 % of this area
Allegheny Formation - Interbedded sandstone, siltstone, claystone, shale, and coal beds; Upper Freeport coal at top; where present, Brookville coal defines base; thickness 275 feet in northeast, increases to 325 feet in south and west. And Pottsville Formation - Interbedded sandstone, siltstone, claystone, shale, and coal beds; conglomeratic orthoquartzite and protoquartzite at base; thickness 60 feet in northeast, increases to 440 feet in southwest
Lithology: sandstone; shale; claystone; siltstone; coal; limestone
Hampshire Formation (Devonian) at surface, covers < 0.1 % of this area
Hampshire Formation - Interbedded red shale, red mudstone, and red to brown cross-bedded siltstone and sandstone; some thin green shale; greenish-gray sandstone and shale toward top; fragmentary plant fossils; thickness 1,400 to 2,000 feet in west, increases to 3,800 feet in east.
Lithology: shale; sandstone; mudstone; siltstone
Greenbrier Formation (Mississippian) at surface, covers < 0.1 % of this area
Greenbrier Formation - Upper part red calcareous shale and sandstone interbedded with greenish-gray and reddish-gray argillaceous limestone; Loyalhanna Limestone Member: Gray to red, cross-bedded, arenaceous calcarenite; total thickness 200 to 300 feet.
Lithology: limestone; sandstone; shale; calcarenite
Catskill Formation (Devonian) at surface, covers 4 % of this area
Catskill Formation - Grayish-red sandstone, siltstone, shale, and mudstone; locally conglomeratic; contains gray sandstone in upper part; lithologies arranged in fining-upward cycles; equivalent to the Hampshire Formation south of Pennsylvania.
Lithology: sandstone; siltstone; shale; mudstone; conglomerate
Monongahela Group (Pennsylvanian) at surface, covers 1 % of this area
Monongahela Group - Cyclic sequences of limestone, shale, sandstone, and coal; commercial coals present; base is at bottom of Pittsburgh coal.
Lithology: limestone; shale; sandstone; coal
Glenshaw Formation (Pennsylvanian) at surface, covers 27 % of this area
Glenshaw Formation - Cyclic sequences of shale, sandstone, red beds, and thin limestone and coal; includes four marine limestone or shale horizons; red beds are involved in landslides; base is at top of Upper Freeport coal.
Lithology: shale; sandstone; limestone; clastic; coal
Mauch Chunk Formation (Mississippian) at surface, covers < 0.1 % of this area
Mauch Chunk Formation - Red and green shale, reddish-purple mudstone, and red, green, brown, and gray thin-bedded and cross-bedded sandstones; thickness 500 feet in west, increases to about 800 feet in east.
Lithology: shale; mudstone; sandstone
Pottsville Formation (Pennsylvanian) at surface, covers 10 % of this area
Pottsville Formation - Predominantly gray sandstone and conglomerate; also contains thin beds of shale, claystone, limestone, and coal; includes Olean and Sharon conglomerates of northwestern Pennsylvania; thin marine limestones present in Beaver, Lawrence, and Mercer Counties; minable coals and commercially valuable high-alumina clays present locally.
Lithology: sandstone; conglomerate; shale; siltstone; claystone; limestone; coal
Scherr Formation (Devonian) at surface, covers 0.7 % of this area
Scherr Formation - Chiefly siltstone; some fine-grained sandstone, shale, and mudstone; light olive gray; marine fossils.
Lithology: siltstone; sandstone; shale; mudstone
Burgoon Sandstone (Mississippian) at surface, covers 3 % of this area
Burgoon Sandstone - Buff, medium-grained, crossbedded sandstone; includes shale and coal; in places, contains conglomerate at base; contains plant fossils; equivalent to Pocono Formation of Ridge and Valley province.
Lithology: sandstone; conglomerate; shale; coal
Shenango Formation through Oswayo Formation, undivided (Mississippian and Devonian) at surface, covers < 0.1 % of this area
Shenango Formation through Oswayo Formation, undivided - Greenish-gray, olive, and buff sandstone and siltstone, and gray shale in varying proportions; includes "Pocono" ("Knapp") and Oswayo of earlier workers; difficult lithologic distinction between Oswayo and "Knapp"- "Pocono" south and east of type area at Olean, N. Y.; contains marine fossils; includes lateral equivalents of Shenango Formation, Cuyahoga Group, Corry Sandstone, Bedford Shale, and Cussewago Sandstone, plus Oswayo Formation.
Lithology: sandstone; siltstone; shale
Allegheny Formation (Pennsylvanian) at surface, covers 28 % of this area
Allegheny Formation - Cyclic sequences of sandstone, shale, limestone, clay, and coal; includes valuable clay deposits and Vanport Limestone; commercially valuable Freeport, Kittanning, and Brookville-Clarion coals present; base is at bottom of Brookville-Clarion coal.
Lithology: sandstone; shale; limestone; clay or mud; coal
Pocono Formation (Mississippian) at surface, covers 0.3 % of this area
Pocono Formation - Light-gray to buff or light-olive-gray, medium-grained, crossbedded sandstone and minor siltstone; commonly conglomeratic at base and in middle; medial conglomerate, where present, is used to divide into Mount Carbon and Beckville Members; equivalent to Burgoon Sandstone of Allegheny Plateau.
Lithology: sandstone; siltstone; conglomerate
Rockwell Formation (Mississippian and Devonian) at surface, covers 1 % of this area
Rockwell Formation - Buff, fine- to medium-grained, crossbedded, argillaceous sandstone and dark-gray shale; includes some carbonaceous shale, sporadic conglomerate beds, and diamictite; included in lower "Pocono" of earlier workers.
Lithology: sandstone; shale; conglomerate

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