This paper summarizes stratigraphic information obtained in a field study of Upper Devonian and lower Mississippian rocks of northeastern Ohio and northwestern Pennsylvania. The upper part of the Chagrin shale has been traced from northeastern Ohio into the Riceville shale in northwestern Pennsylvania. The Cleveland member of the Ohio shale has been traced from its type locality near Cleveland eastward into the Grand River valley in western Ashtabula County, Ohio, where the black shale of the Cleveland appears to grade laterally into the upper part of the gray Chagrin shale. The Bedford shale and the Berea sandstone have been traced eastward from northern Ohio to the vicinity of Meadville in central Crawford County, Pennsylvania. The Bedford shale is underlain by the Cleveland member of the Ohio shale west of the Grand River valley and by the Cussewago sandstone in extreme northeastern Ohio and in northwestern Pennsylvania east of Meadville. The Cussewago sandstone, which forms a good key bed, is not a part of the Berea sandstone as has been suggested previously by some geologists. The Cussewago sandstone was derived from a different source and deposited from a different direction than either the Berea sandstone or the Corry sandstone. In northwestern Pennsylvania, the Bedford shale was found to be the same as White's Cussewago shale and Chadwick's Hayfield shale. In the vicinity of Meadville, Pennsylvania, the Bedford shale and the Berea sandstone grade laterally into a thin unit of siltstones and intercalated shale, here named the Shellhammer Hollow formation. Farther east, near Riceville, Pennsylvania, the Shellhammer Hollow formation grades laterally eastward into the Corry sandstone. The Corry sandstone, therefore, can not be considered an eastern siltstone facies of the Berea sandstone as has been suggested previously, although it is a near temporal equivalent of the Berea sandstone. A very coarse-grained deltaic sandstone occurs above the stratigraphic horizon of the Corry sandstone in part of southeastern Erie County, Pennsylvania. This local sandstone is here named the Hungry Run sandstone member of the Orangeville shale. A thin silt-stone, characterized by many short curved markings, is an excellent stratigraphic marker in the basal part of the Orangeville shale, above the Berea sandstone, the Shellhammer Hollow formation, and the Corry sandstone. This siltstone, here named the Bartholomew siltstone member, has been traced widely over southern Erie County, Crawford County, and northwestern Venango County, Pennsylvania.