214 H. p. GUSHING UNCONFORMITY AT BASE OF BEREA GRIT 



At the base of the Berea we utterly miss this sort of evidence. The 

 underlying horizon is unvarying. To be sure, when we pass out of Ohio 

 the Berea is found resting on the Chagrin formation, in the comities of 

 western Pennsylvania. To Ulrich and myself the Bedford absence there 

 seems a ease of overlap. It is absent because it was never deposited there, 

 the district lying without its basin. Prosser does not accept this view, 

 but holds, if I understand him correctly, that the Bedford disappears by 

 lateral gradation into beds which carry a Chemung fauna. The sections 

 are scattered and poor and the evidence incomplete either way; but to 

 the writer it seems a clear case of overlap. Along the Ohio-Pennsylvania 

 line there seems to have been a barrier formed between two separate 

 troughs of deposit. On the Pennsylvania side the EJiapp and Conewango 

 formations were laid down on the Chemmig, but did not get into Ohio to 

 any extent. On the Ohio side the Bedford was deposited, but failed to 

 pass over into Pennsylvania. Along the barrier both substantially fail 

 and the Berea lies on the Chagrin. It so lies not because of erosion of 

 the other formations, but because they were never deposited there. 



It is frankly admitted that the above interpretation does not meet the 

 views of many geologists. It seems to us, however, that we may also 

 waive this and not greatly affect the force of our contention that the 

 uniform resting of the Berea on the thin and weak Bedford formation 

 ail across Ohio makes it exceedingly improbable that their contact can 

 mark a time interval of any particular import^ance. 



Prosser has described a Berea-Bedford contact at Warner Hollow, 

 Ashtabula County, where the upper Bedford has been slightly crimipled 

 and also slightly faulted before Berea deposition began.'' He emphasizes 

 the locality as of exceptional importance in demonstrating a disconform- 

 ity, between the two formations. AVe can not see it in the same light. 

 The disturbance is exceedingly local and exceedingly small in amount. 

 The locality is not many miles west of the meridian along which the Bed- 

 ford disappears, hence near what we regard as its eastern shoreline. Very 

 trifling local causes could produce disturbances of this character in uncon- 

 solidated muds and sands. It seems to us to have no weight whatever in 

 comparison with the great general fact that the Berea base j^ractically 

 does not change horizon all across Ohio, but rests everywhere on the tliin 

 Bedford shale. 



In Kentucky the Berea disappears by overlap. It may also be noted 

 that the Bedford is a partner in this transaction, the two both thinning 

 and pinching out together, letting the Sunbury black shale down on the 



» Bull. 15, Geol. Surv. Ohio, pp. 312-315. 



