The practically continuous area of Monongahela is confined to the southwest four counties of Pennsylvania, a narrow strip in eastern Ohio, and central West Virginia. Small outlying patches remain east from the Alleghenies, in the First and Second basins of Pennsylvania, and, at the south, beyond the Kanawha river in West Virginia. The area in which this formation remains is far within that of the Conemaugh, except at the east.
The formation, as limited by Doctor I. C. White, has the Pittsburg coal bed as the lowest and the Waynesburg coal bed as the highest stratum. The thickness varies from somewhat more than 400 feet in central West Virginia to about 140 feet at the most northerly exposure in Jefferson county of Ohio. This formation is characterized by notable variation in thickness of intervals and in composition of the rocks, as well as by local irregularities . . .