The Marcellus Shale is a dark shale, commonly called a black shale, that can be found in parts of Ohio, West Virginia, Pennsylvania, and New York. It was deposited in what was a shalow sea around 390 million years ago during the Devonian period. Marcellus Shale is mostly located deep beneath Earth’s surface, but because the layers of rock are tilted toward the south, the Marcellus is deeper in the south and is exposed at the surface near the north end of the Finger Lakes region.