UNDERLYING FORMATION 200 



the change of conditions from mud to sand deposit; but it seems to me 

 of distinctly the same type as the channeling at the base of the Berea. 



In central Ohio there are some sandy beds near the summit of the 

 Berea, so much so that there have been differences of opinion as to where 

 to place the line between the two. Prosser thinks these sandy beds have 

 been eroded away over areas of considerable extent prior to Berea deposi- 

 tion, and argues a time interval of considerable extent between the two 

 to account for this erosion. The writer is unfamiliar with those sections, 

 but in conversation with other geologists, who do know the region, ex- 

 pressed interpretations of the phenomena did not correspond with Pros- 

 ser's interpretation. 



Below the Bedford lies the Cleveland shale, a black, slaty shale, which 

 today is a much more resistant formation than the Bedford ; but it 

 breaks down rapidly on exposure to the weather, when exposed in banks, 

 and certainly is not a formation of any particular resistance to erosion 

 as compared with ordinary sandstones and limestones. In the post- 

 glacial valleys of the small streams in northern Ohio an excellent idea of 

 the erosional resistance of this formation can be obtained. It comes into 

 the problem at all only because the deep channels of the northwest dis- 

 trict cut into it. 



Beneath the Cleveland in the eastern sections lies the gray Chagrin 

 shale. It is weak, but the Berea erosion nowhere reaches it. West of 

 Cleveland a blackish shale, with occasional blue bands, lies beneath and 

 is a weaker rock than the typical Cleveland shale. The bottoms of the 

 deeper western channels are in this rock. 



Extent of the Berea Sandstone 



The Berea extends out of Ohio into Michigan on the north, Kentucky 

 on the south, and Pennsylvania on the east. In Michigan it is kno\\Ti 

 only on the east side of the Carboniferous basin and does not show in 

 outcrop. Lane, from study of the drill records, reports it as varying in 

 thickness from 40 to over 300 feet, as being thickest and coarsest on the 

 west, and then suddenly disappearing.^ In all probability this means 

 also the occurrence of channels similar to those on the northwest in Ohio, 

 perhaps somewhat deei)er, since the greatest known tliickness in Ohio 

 does not much exceed "iOO feet. Lane states that the Michigan Berea 

 forms a deposit along a shore facing east and running nearly north- 

 sduth, and this corresponds well to the Oliio conditions. 



" Jour. Geol., vol. 18, p. 418. 



