The

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, w ...

Foreknobs Formation is a mapped

bedrock In geology, bedrock is solid rock that lies under loose material ( regolith) within the crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface material. An exposed portion of be ...

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, Ma ...

Maryland Maryland ( ) is a U.S. state, state in the Mid-Atlantic (United States), 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; ...

Virginia Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the East Coast of the United States, Atlantic Coast and the Appalachian Mountains. The geography an ...

, and

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 ...

Description

The Foreknobs Formation contains massive

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, ...

; "redbeds" of brownish-gray sandstone, siltstone, and

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especia ...

containing scattered marine fossils; and occasional quartz-pebble conglomerate or conglomeratic sandstone beds.

Stratigraphy

Dennison (1970) renamed the old Chemung Formation the Greenland Gap Group and divided it into the lower

Scherr Formation The Devonian Scherr Formation is a mapped bedrock unit in Pennsylvania, Maryland, Virginia and West Virginia. Description The Scherr Formation consists predominantly of siltstone and shale. Lower part of unit includes considerable fine-grained san ...

and the upper Foreknobs Formation. De Witt (1974) extended the Scherr and Foreknobs into Pennsylvania, but did not use the term Greenland Gap Group. Boswell, et al. (1987), does not recognize the Scherr and Foreknobs Formations in the subsurface of West Virginia and thus these formations are reduced from "group" to "formation" as the Greenland Gap Formation. Rossbach and Dennison (1994) extended the Foreknobs into the Catawba syncline of southwestern Virginia.Rossbach, T.J., and Dennison, J.M., 1994, Devonian strata of Catawba syncline, near Salem, Virginia, IN Schultz, Art, and Henika, Bill, Fieldguides to Southern Appalachian structure, stratigraphy, and engineering geology: Virginia Polytechnic Institute and State University, Department of Geological Sciences Guidebook, Geological Society of America, Southeastern Section, Annual Meeting, Blacksburg, VA, April 7–9, 1994, no. 10, p. 95-126. The Foreknobs is divided into the following Members, in ascending order: Mallow Member, Briery Gap Sandstone Member, Blizzard Member, Pound Sandstone Member, and Red Lick Member

Fossils

Red beds within the Foreknobs contain scattered marine fossils, such as

brachiopod Brachiopods (), phylum Brachiopoda, are a phylum of trochozoan animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, ...

Notable Exposures

Type section: along WV Highway 42, 0.48 km northwest of Scherr,

Grant County, West Virginia Grant County is a county in the U.S. state of West Virginia. As of the 2020 census, the population was 10,976. Its county seat is Petersburg. The county was created from Hardy County in 1866 and named for Civil War General Ulysses S. Grant. H ...

Age

Relative age dating places the Foreknobs in the

Late Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

References

Sandstone formations of the United States Shale formations of the United States Siltstone formations Devonian Maryland Devonian geology of Pennsylvania Devonian geology of Virginia Devonian West Virginia Geologic formations of Maryland Geologic formations of Pennsylvania Geologic formations of Virginia Geologic formations of West Virginia Devonian southern paleotemperate deposits {{Maryland-geologic-formation-stub