The Devonian Harrell Formation is a mapped bedrock unit in Pennsylvania, Maryland, West Virginia, and Virginia.
Hasson and Dennison (1978) state "The Harrell Shale consists of very dark gray, thinly laminated, platy- to sheety-weathering shale underlain in certain areas by the grayish black shale of the Burket Member.
"[3] Hasson and Dennison reported the following fossils from several outcrops of the Harrell:[3] Type locality is at Horrell Station, Blair County, Pennsylvania (40°27′N 78°17′W / 40.450°N 78.283°W / 40.450; -78.283).
[2] In 1918, when Butts described and named the type section, the USGS topo map spelled the location "Harrell", [4] but the local spelling was "Horrell".
[5][6] Relative age dating places the Harrell in the late Devonian.