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Geologic units in Fayette county, Pennsylvania

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.

Glenshaw Formation (Pennsylvanian) at surface, covers 19 % 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.

Monongahela Group (Pennsylvanian) at surface, covers 16 % 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

Waynesburg Formation (Permian and Pennsylvanian) at surface, covers 10 % of this area

Waynesburg Formation - Cyclic sequences of sandstone, shale, limestone, and coal; commercial coals present; base is at bottom of Waynesburg coal.

Lithology: sandstone; shale; limestone; coal

Pottsville Formation (Pennsylvanian) at surface, covers 7 % 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.

Burgoon Sandstone (Mississippian) at surface, covers 6 % 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.

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.

Washington Formation (Permian) at surface, covers 5 % of this area

Washington Formation - Cyclic sequences of sandstone, shale, limestone, and coal; includes some red shale; base is at bottom of Washington coal.

Lithology: sandstone; shale; limestone; coal

Shenango Formation through Oswayo Formation, undivided (Mississippian and Devonian) at surface, covers 2 % 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

Casselman Formation (Pennsylvanian) at surface, covers 1 % 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.

Catskill Formation (Devonian) at surface, covers 0.4 % 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.

Greene Formation (Permian) at surface, covers 0.2 % of this area

Greene Formation - Cyclic sequences of sandstone, shale, red beds, thin limestone, and thin, impure coal; base is at top of Upper Washington limestone.

Lithology: sandstone; shale; limestone; coal

Foreknobs Formation (Devonian) at surface, covers 0.2 % 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.