REVIEW OF THE STRATIGRAPHY OF THE FOSSIL- 



IFEROUS MEMBERS OF THE POTTSVILLE 



FORMATION i BELOW THE LOWER 



MERCER LIMESTONE 



PENNSYLVANIA SYSTEM 



The rocks of the Pennsylvanian system outcrop in southeastern 

 Ohio over an area of approximately 11,125 square miles. They are 

 divided into four formations: the Pottsville, Allegheny, Conemaugh, 

 and Monongahela, and together their entire thickness in the State 

 averages 1,100 feet. The present report deals only with the oldest 

 formation of the Pennsylvanian system, the Pottsville. 



Pottsville Formation 



The Pottsville formation, occurring at the base of the Pennsyl- 

 vanian system, includes all the rocks between the Mississippian 

 system below and the Allegheny formation of the Pennsylvanian 

 system above; or between the Maxville limestone, or the Waverly 

 formation where the former is wanting, and the Brookville coal, 

 which forms the basal member of the Allegheny formation. In 

 many places, especially in the central part of the outcrop, there is 

 no sharp line of demarcation between the Pottsville and Allegheny 

 formations, as shales form the upper members of the Pottsville and 

 the lower members of the Allegheny, so that there is a gradual trans- 

 ition from one formation to the other. The outcrop of the formation 

 is extensive and crosses the southeastern portion of the State, border- 

 ing the younger Pennsylvanian formations on the west, northwest, 

 and north. Beginning at the Ohio River in Scioto and Lawrence 

 counties, the rock exposures extend northeastward as far as Wayne 

 and Stark counties, and then eastward crossing the Ohio-Pennsylvania 

 state line from Mahoning County. The formation is found in the 

 following counties: Lawrence, Scioto, western Gallia, Jackson, eastern 

 Pike, Vinton, western Athens, Hocking, Perry, Muskingum, eastern 

 Licking, Coshocton, eastern Knox, Tuscarawas, Holmes, Wayne, 

 Stark, eastern Medina, Summit, Geauga, Portage, southern Trumbull, 

 and Mahoning. 



Between the Mississippian and Pennsylvanian systems, or at 

 the base of the Pottsville formation, there exists everywhere a great 

 unconformity, as is shown by the extremely irregular upper surface 

 of the Mississippian rocks. The basal members of the Pottsville 

 formation rest sometimes on varying thicknesses of Maxville lime- 

 stone and sometimes directly upon the Logan formation which occurs 

 below the Maxville limestone. The Maxville limestone is found in 

 patches, which, as shown by W. C. Morse, are undoubtedly the rem- 



!The main divisions of the Pennsylvania system the Pottsville, Allegheny, Conemaugh, and 

 Monongahela are here given the rank of formations, while the subdivisions of each are called members, 

 according to the usage adopted by the Geological Survey of Ohio. In other States, different values are 

 sometimes assigned to the divisions of the Pennsylvanian system. 



