The New Creek Limestone, which is very thick to the north, is very thin and is typically micritic. The underlying Keyser Limestone is a fossiliferous, coarse-grained limestone. The Silurian-Devonian systemic boundary is within the Keyser. Interbedded laminated argillaceous limestone and minor calcareous shale, usually dark gray in color. The laminated beds weather out as slabs or plates.
Fossils are uncommon, but occasional layers of ostracods and stromatolites can be found.
Mostly dark calcareous shales with some interbedded dark, argillaceous limestones. Some outcrops contain olive-green shales similar to the upper Rose Hill Fm. This formation weathers very easily and is not well exposed in the field camp mapping areas. This sandstone is informally called the Rainbow Run Sandstone Member of the Wills Creek Formation. At some localities a zone of ostracods can be found at the base in interbedded shale and sandstone.