Geologic units in Venango county, Pennsylvania

Pottsville Formation (Pennsylvanian) at surface, covers 56 % of this area

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.

Shenango Formation (Mississippian) at surface, covers 19 % of this area

Light-gray sandstone and some beds of medium-gray shale and siltstone; upper third of formation is more shaly; contains a few marine fossils.

Allegheny Formation (Pennsylvanian) at surface, covers 14 % of this area

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.

Cuyahoga Group (Mississippian) at surface, covers 9 % of this area

Medium-gray siltstone and dark-gray shale containing interbedded light-gray, flaggy sandstone. Includes, in descending order: Meadville Shale, Sharpsville Sandstone, and Orangeville Shale; marine fossils common.

Corry Sandstone through Riceville Formation, undivided (Devonian) at surface, covers 1 % of this area

Same as Berea-through-Riceville (MDbr) interval, but uppermost sandstone unit is recognized as Corry, not Berea.

Burgoon Sandstone through Cuyahoga Group, undifferentiated (Mississippian) at surface, covers 0.7 % of this area

Informal unit including elements of Burgoon Sandstone and Shenango Formation plus Cuyahoga Group; correlation uncertain; contains sedimentary structures and trace fossils characteristic of tidal flats; called ""Pocono"" by earlier workers.

Shenango Formation through Cuyahoga Group, undivided (Mississippian) at surface, covers 0.1 % of this area

Includes the Shenango Formation (Ms) and Cuyahoga Group (Mc), which are described separately below. Shenango: Light-gray sandstone and some beds of medium-gray shale and siltstone; upper third of formation is more shaly; contains a few marine fossils. Cuyahoga: Medium-gray siltstone and dark-gray shale containing interbedded light-gray, flaggy sandstone. Includes, in descending order: Meadville Shale, Sharpsville Sandstone, and Orangeville Shale; marine fossils common.