The Glenshaw Formation is a mapped

sedimentary Sedimentary rocks are types of rock (geology), rock that are formed by the accumulation or deposition of mineral or organic matter, organic particles at Earth#Surface, Earth's surface, followed by cementation (geology), cementation. Sedimentati ...

bedrock unit in

Pennsylvania Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...

Maryland Maryland ( ) is a state in the Mid-Atlantic region of the United States. It shares borders with Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware and the Atlantic Ocean to ...

West Virginia West Virginia is a state in the Appalachian, Mid-Atlantic and Southeastern regions of the United States.The Census Bureau and the Association of American Geographers classify West Virginia as part of the Southern United States while the Bur ...

, and

Ohio Ohio () is a state in the Midwestern region of the United States. Of the fifty U.S. states, it is the 34th-largest by area, and with a population of nearly 11.8 million, is the seventh-most populous and tenth-most densely populated. The sta ...

, of Pennsylvanian age. It is the lower of two formations in the Conemaugh

Group A group is a number of persons or things that are located, gathered, or classed together. Groups of people * Cultural group, a group whose members share the same cultural identity * Ethnic group, a group whose members share the same ethnic iden ...

, the upper being the

Casselman Formation The Casselman Formation mapped sedimentary bedrock unit in Pennsylvania, Maryland, and West Virginia, of Pennsylvanian age. It is the uppermost of two formations in the Conemaugh Group, the lower being the Glenshaw Formation. The boundary bet ...

. The boundary between these two units is the top of the marine Ames Limestone. The Conemaugh Group overlies the Upper Freeport coal bed of the

Allegheny Formation The Pennsylvanian Allegheny Formation is a mapped bedrock unit in western and central Pennsylvania, western Maryland and West Virginia, and southeastern Ohio. It is a major coal-bearing unit in the Appalachian Plateau of the eastern United States ...

and underlies the

Pittsburgh coal seam The Pittsburgh Coal Seam is the thickest and most extensive coal bed in the Appalachian Basin; hence, it is the most economically important coal bed in the eastern United States. The Upper Pennsylvanian Pittsburgh coal bed of the Monongahela Grou ...

of the

Monongahela Group The Monongahela Formation is a geologic formation in West Virginia, Pennsylvania, Ohio, and Maryland. It preserves fossils dating back to the Carboniferous and Permian periods. See also * List of fossiliferous stratigraphic units in West Virgin ...

. The Conemaugh Group consists of cyclic sequences of shale, siltstone, sandstone, red beds, thin impure limestone, and thin nonpersistent coal. Red beds are associated with landslides. The thickness of the Conemaugh Group averages about 400 feet in Ohio, and it ranges from 450 feet on the Ohio River in West Virginia to 520 feet in Washington County, Pennsylvania, and then to 890 feet in Somerset County, Pennsylvania. The Glenshaw formation was originally mapped in Pennsylvania by Flint, but was extended into West Virginia by Cardwell ''et al.'' in 1968. It is also recognized in eastern Ohio.Rice, C.L., Hiett, J.K., and Koozmin, E.D., 1994, Glossary of Pennsylvanian stratigraphic names, central Appalachian basin, IN Rice, C.L., ed., Elements of Pennsylvanian stratigraphy, central Appalachian basin: Geological Society of America Special Paper, 294, p. 115-155.

Footnotes

Carboniferous Kentucky Geologic formations of Pennsylvania Geologic formations of Maryland Carboniferous West Virginia Carboniferous Ohio Pennsylvanian Series Carboniferous geology of Virginia Carboniferous southern paleotropical deposits {{Maryland-geologic-formation-stub