PART I 



STRATIGRAPHY OF THE FOSSILIFEROUS 



MEMBERS OF THE POTTSVILLE 



FORMATION 1 



PENNSYLVANIAN 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, Pottsville, Allegheny, Conemaugh, and 

 Monongahela, and together their entire thickness in the State averages 

 1,100 feet. This bulletin 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 Alle- 

 gheny, so that there is a gradual transition from one formation to the 

 other. The outcrop of the formation is extensive and crosses the 

 southeastern portion of the State. Beginning at the Ohio River in 

 Scioto and Lawrence counties, the rock exposures extend northeast- 

 ward as far as Wayne and Stark counties, and then eastward, crossing 

 the Ohio-Pennsylvania State line from Mahoning County. The forma- 

 tion 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, Mahoning, and Columbiana. 



J The main divisions of the Pennsylvanian 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. 



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