10 POTTS VILLE FAUNA OF OHIO 



to remove most of the Maxville limestone, and in some places for 

 streams to cut into the underlying Logan formation. Remnants of 

 the Maxville limestone appear at the present time only as isolated 

 patches or islands surrounded by younger rocks of Pottsville age. At 

 the end of these land conditions, the region was again submerged and 

 the basal members of the Pottsville formation, the Harrison ore and 

 the Sharon conglomerate, were deposited in the low troughs and basins. 



The Pottsville formation varies in thickness from 100 to 350 feet 

 but averages about 255. The deposit thickens toward the south, and 

 in southern Ohio attains its maximum development; there is also a 

 general thickening from the western to the eastern part of the outcrop. 

 The extremely irregular line of contact between the Pottsville forma- 

 tion and the Mississippian system below is responsible for the great 

 variation in the thickness of the formation in different regions. Where 

 the Maxville limestone has been largely or entirely eroded, the lowest 

 members of the Pottsville formation, the Harrison ore and the Sharon 

 conglomerate, are present, while successively higher members form the 

 base of the formation where increasing thicknesses of Maxville lime- 

 stone are found. In Hopewell Township, Muskingum County, on 

 Poverty Run, the Quakertown coal forms the base of the Pottsville, 

 while elsewhere any of the horizons from the Harrison ore to the Quaker- 

 town coal may be in -contact with rocks of Mississippian age. 



The Pottsville formation in Ohio is composed for the most part of 

 shales and sandstones, interbedded with clays, coals, iron ores, and 

 marine limestones. The accompanying generalized section of the 

 formation shows the succession of the various members and their rela- 

 tions to each other. The members vary greatly in character and 

 thickness from place to place. Some, such as the Black Flint at the 

 top of the formation, are local in their occurrence and are found only 

 in the southern part of the outcrop; others, such as the Me Arthur 

 limestone and Sciotoville clay, are more extensively developed in 

 southern Ohio but to the northward become thin and finally disappear. 

 There are certain strata, however, of great importance for stratigraphic 

 study, as they are very persistent and can be traced from the Ohio 

 River northward along the Pottsville outcrop to the Ohio-Pennsylvania 

 state line. At the base occurs the Sharon conglomerate which, al- 

 though patchy in appearance, can be found everywhere in the deepest 

 troughs eroded in pre-Pottsville times. Among the coals, the Quaker- 

 town or No. 2 coal, the Lower Mercer or No. 3 coal, the Middle Mercer 

 or No. 3a coal, and the Tionesta or No. 3b coal are the well-defined 

 stratigraphic units. By far the best developed and most persistent 

 horizons, however, are the Lower and Upper Mercer limestones with 

 their accompanying iron ores; these members, especially the Lower 

 Mercer, are found in every county where they may be expected, and 



