Under the true Carboniferous strata of Ohio, that is below the base of the Berea Grit, lies a mass of shale of varying colour many hundred feet in thickness. The uppermost fifty or sixty feet are often red or reddish, and have been separated with the name of the Bedford Shale. The next layer, of about the same thickness, is usually black or at least very dark and bears the name of the Cleveland Shale. Below this again is a greenish mass 500 feet or more in thickness, known as the Erie Shale. Another dark bed follows—the Huron Shale—beneath which is the great limestone base of the Devonian in Ohio, the Corniferous.