Wills Creek Formation

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Wills Creek Formation
Stratigraphic range: Silurian
Wills Creek Fm fold.jpg
Tight anticlinal fold in the Wills Creek Formation, along Route 22, Neff, Huntingdon County, Pennsylvania
Type sedimentary
Underlies Tonoloway Formation
Overlies Bloomsburg Formation and Williamsport Formation
Primary sandstone, shale
Other siltstone, limestone, dolostone
Region Appalachian Mountains
Extent Pennsylvania, Maryland, Virginia, West Virginia
Type section
Named for Wills Creek at Cumberland, Allegany County, Maryland
Named by P. R. Uhler, 1905[1]

The Silurian Wills Creek Formation is a mapped bedrock unit in Pennsylvania, Maryland, Virginia, and West Virginia.


The Wills Creek is defined as a moderately well bedded greenish-gray shale containing local limestone and sandstone zones, or more specifically as an olive to yellowish-gray, thin-bedded sandstone, calcareous shale, dolostone, argillaceous limestone, and sandstone. Red shale and siltstone occur in the lower part of the formation. The formation has a thickness between 450 feet and 600 feet in Maryland and 445 to 620 feet in Pennsylvania.[2]

The Wills Creek forms the bedrock of the valley around and to the east of Lewistown, Pennsylvania.[3]


The Wills Creek Limestone contain fossils from the Pridoli to the Ludlow epoch, or 422.9 to 418.1 Ma.[4]

Dean et al. (1985) describe the Wills Creek as sparsely fossiliferous.[5]

Conodonts have been identified in the Wills Creek in Virginia (Ozarkodina snajdri crispa Zone).[6]

Notable Exposures[edit]


Relative age dating of the Wills Creek places it in the Silurian period. It rests conformably a top the Bloomsburg Formation and below the Tonoloway Formation.[7]

Economic Uses[edit]

The Wills Creek is a poor source of construction material and is only suitable as common fill.[8]


  1. ^ Uhler, P.R., 1905, The Niagara period and its associates near Cumberland, Maryland: Maryland Academy of Science Transactions, v. 2, p. 19-26.
  2. ^ "Table 1. Paleozoic Stratigraphic Section in Central Pennsylvania" (PDF). Geological Report On The Skytop Road Cuts. Pennsylvania State University Department of Geosciences. 2004. 
  3. ^ McElroy, Thomas A. (2004). Bedrock Geologic Map of the Lewistown Quadrangle, Mifflin and Juniata Counties, Pennsylvania (pfd) (Map). Pennsylvania Geological Survey. 
  4. ^ "Wills Creek Limestone Formation". The Paleobiology Database. Advisory Board of the Paleobiology Database. Retrieved 2008-01-26. 
  5. ^ Dean, S.L., Kulander, B.R., and Lessing, Peter, 1985, Geology of the Capon Springs, Mountain Falls, Wardensville, Woodstock, and Yellow Springs quadrangles, Hampshire and Hardy Counties, West Virginia: West Virginia Geological and Economic Survey Map, 26, 1 sheet, scale 1:24,000
  6. ^ Harris, A.G., Stamm, N.R., Weary, D.J., Repetski, J.E., Stamm, R.G., and Parker, R.A., 1994, Conodont color alteration index (CAI) map and conodont-based age determinations for the Winchester 30' x 60' quadrangle and adjacent area, Virginia, West Virginia, and Maryland: U.S. Geological Survey Miscellaneous Field Studies Map, MF-2239, 40 p., 1 sheet, scale 1:100,000 [1]
  7. ^ "Allegheny Plateau and Valley and Ridge". Geologic Map of Maryland. Maryland Geological Survey. 1968. Retrieved 2008-01-26. 
  8. ^ Doden, Arnold G. & Gold, David P. (2008). "Bedrock Geologic Map of The Mc Alevys Fort Quadrangle, Huntingdon, Centre, and Mifflin Counties, Pennsylvania" (pdf). Pennsylvania Geological Survey. 

See also[edit]