The Middle Run Formation is a

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

Ohio Ohio ( ) is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders Lake Erie to the north, Pennsylvania to the east, West Virginia to the southeast, Kentucky to the southwest, Indiana to the ...

. It dates back to the

Precambrian The Precambrian ( ; or pre-Cambrian, sometimes abbreviated pC, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of t ...

. It was discovered in October 1987 when the

United States Geological Survey The United States Geological Survey (USGS), founded as the Geological Survey, is an agency of the U.S. Department of the Interior whose work spans the disciplines of biology, geography, geology, and hydrology. The agency was founded on Mar ...

dug a sample to learn more about Ohio's Precambrian basement rocks. Scientists estimated the boundary to be at 3,500 ft below the surface. After drilling through Mt. Simon sandstone, past the 3,500 ft mark, they were surprised to find more sandstone, which is the Middle Run Formation. Drilling in 1989 reached a depth of 5,370 ft of this same formation before the drill bit was stuck—without reaching the Precambrian basement rocks.

References

Generalized Stratigraphic Chart for Ohio
Geology of Ohio Proterozoic Eonothem of North America {{ohio-geologic-formation-stub