The Marcellus Formation or the Marcellus Shale is a Middle Devonian age unit of sedimentary rock found in eastern North America. Named for a distinctive outcrop near the village of Marcellus, New York, in the United States,
it extends throughout much of the Appalachian Basin.
The unit name usage by the U.S. Geological Survey includes Marcellus Shale and Marcellus Formation. From Wikipedia
