to the Ohio Shale Problem. 169 



be more widely and more evenly distributed than either of the 

 underlying members of the Ohio shale. As already said, it 

 extends as a practically continuous sheet at the top of the Ohio 

 shale division of the Chattanoogan from Lake Erie to Alabama. 

 Here and there across this wide area it may be absent, in some 

 cases evidently because it had pinched out by overlap on some 

 old uplift. In other places, however, it may have been thinned 

 and occasionally cut through by erosional processes prior to or 

 during the areally more limited deposition of the succeeding 

 Bedford and Berea. 



Bedford shale. — This formation consists largely of light- 

 blue or gray shales in part often reddened, especially near the 

 base though also toward the top, with peroxide of iron. Com- 

 monly line-grained sandstones, usually in thin layers, and often 

 beautifully ripple-marked, are interbedded with the shales, but 

 occasionally similar arenaceous matter forms irregular masses. 

 The Bedford outcrops apparently in a continuous band across 

 the state of Ohio, ranging in thickness between 50 and 100 

 feet. South of the Ohio it gradually pinches out along the 

 line of outcrop, being unknown beyond Irvine, Kentucky. In 

 an easterly and .southeasterly direction from north central 

 Ohio the formation probably extends underground into the 

 neighboring states of Pennsylvania and West Virginia. In 

 the logs of deep wells it is usually included with the underly- 

 ing Ohio shales. 



Berea grit. — In that it is intercalated between two bodies of 

 shale, and hence easily recognizable, this extraordinarily per- 

 sistent sandstone constitutes an extremely valuable datum 

 plane in Ohio geology. In Lorain County the Berea is 

 thicker than usual, locally attaining 225 feet. Elsewhere it 

 seldom exceeds 50 feet. Unusual thicknesses have occasion- 

 ally been reported also in deep wells to the southeast of 

 Lorain County, even as high as 170 feet. In the latter cases it 

 is thought likely that a considerable part of the excess should 

 have been referred to the Bedford rather than the Berea. 

 Commonly the rock is a fine-grained sandstone, usually in thin 

 even layers, frequently ripple-marked, and occasionally with 

 pebbles. Clay is usually present, mostly forming thin seams 

 of shale, but it is never a very important constituent. In 

 Lorain and Cuyahoga counties the sandstone is often of coarser 

 grain and much of it relatively massive. The base evidently 

 marks an unconformity that is locally conspicuous. The top 

 also is very sharply distinguished from the overlying Sunbury 

 shale. Regarding areal distribution, that of the Berea sand- 

 stone seems to be very nearly the same as the Bedford. It 

 extends eastwardly into Pennsylvania and southwardly to Estill 



