34 J. J. STEVENSON — CAKBONIFEROUS OF APPALACHIAN BASIN 



and 68 feet, the interval to the Eedstone coal bed decreasing to 25 feet. 

 The upper coal layers of the Pittsburg disappear northward, but the 

 interval from the "Main" coal to the Eedstone decreases very slowly 

 and becomes normal only as one approaches the north end of the basin. 

 A similar condition exists in southern Fayette within the Lisbon basin, 

 but the divergence as well as the area in which it occurs is not so great; 

 farther west in Pennsylvania and Ohio the tendency to local irregularity 

 of deposit is shown by the presence of "rider" coal beds at many locali- 

 ties. 



The Pittsburg sandstone (H. D. Eogers, 1858) is a variable rock 

 overlying the Pittsburg coal on the borders of the basin, but it is far 

 from being persistent, the interval being filled with shale very fre- 

 quently. A thin deposit of shale usually intervenes between the coal 

 and the sandstone. This coarse deposit is present commonly along the 

 northern outcrop in Pennsylvania as well as in the Connellsville basin 

 and southward in the exposed area of West Virginia; it is important 

 along the southern edge of the field in that state into Ohio, where it is 

 almost constant in Gallia, Meigs, and Morgan counties on the south 

 and west border; but northward from Morgan, on the western border, 

 it is wanting until one comes to western Belmont, Guernsey, and Har- 

 rison. Its distribution in Ohio lends probability to the suggestion al- 

 ready offered respecting the western extent to the Pittsburg coal bed. 

 This sandstone is confined practically to the borders of the field, and 

 within the interior portions one finds shale with only occasional sand- 

 stone in the interval. 



The Eedstone limestone (J. J. Stevenson, 1877) is confined to the 

 north central part of the field, being absent along the northern outcrop 

 in Pennsylvania as well as in nearly the whole of West Virginia and 

 Ohio. Like the other limestones of this formation, it is non-fos- 

 siliferous or at the most contains minute forms which may be of fresh- 

 water types. It persists in Pennsylvania between Chestnut ridge and 

 the Ohio river and is present in eastern Belmont of Ohio; it disappears 

 quickly south from the Pennsylvania line in West Virginia. Perhaps 

 it may be the "limestone group" of Andrews in southeastern Ohio, but 

 that can be no more than a mere suggestion; for, as indicated by Pro- 

 fessor Andrews more than 30 years ago, these limestones appear to be 

 irregular deposits of calcareous mud and are given to sudden variations. 

 Within Pennsylvania and the immediately adjacent part of West Vir- 

 ginia the correlation is exact. 



The Eedstone coal bed (H. D. Eogers, 1858) is very persistent in the 

 northern part of the basin, though rarely attaining sufficient thickness 



