34 W. A. Yerwiehe — Correlation of the 



sent in part tlie Chagrin shale and Cleveland shale ; or is it 

 merely the western equivalent of the Cleveland shale ? 



Fourth: Does the Cleveland shale thin toward the east 

 because of overlap in that direction or does it constitute a 

 variation in facies of the Chagrin formation ? 



Fifth: Does the Bedford have a continuation toward the 

 east in the Chemung rocks to which its fossils allies it, or in 

 the Catskill which is more nearly on the same stratigraphic 

 horizon, or does it thin out by overlap in Ashtabula County? 



Sixth: Is it probable that a disconformity exists at the base 

 of the Bedford and that this explains the discrepancy in the 

 thickness of the shales as they are traced toward the west, and 

 perhaps also the gap in paleontologic evidence which some 

 authorities have mentioned ? 



Seventh : Are the formations of New York, particularly the 

 Hamilton, Portage and Chemung, equally represented in the 

 totally different shales of Ohio ; is one or the other missing 

 entirely ; do they thin down so greatly because of overlap or 

 do they simply ' wedge out ' to a feather edge? 



Finally : How much weight shall be given to the paleon- 

 tological evidence ? H. S. Williams'^ has shown that fossil 

 evidence varies with the lithologic character of the rock and 

 that faunas are frequently recurrent in such typical form as to 

 lead to erroneous conclusions. J. ]M. Clarkef states that the 

 Portage carries a Chemung fauna in the eastern part of New 

 York State. 



It is clear then that paleontologic evidence must be used 

 with extreme caution and at this stage of our knowledge should 

 probably be subordinated to stratigraphic evidence in case of 

 disagreement. 



No one realizes more strongly than the writer that a com- 

 plete answer to these questions is impossible at the present time; 

 however, the new light thrown on the problem by a field study 

 of the formations involved, extending over a period of eight 

 years, certainly justifies a review. 



Devonian Shales of Ohio. 



Bedford: This formation consists of bluish, reddish, and 

 mottled argillaceous shale, with thin sandstones locally devel- 

 oped. It is somewhat fossiliferous especially toward the base, 

 and on the strength of its fossils has been pronounced by 

 several eminent geologists as Devonian in age. Its strati- 

 graphic position also seems to warrant this conclusion. The 

 Mississippian above is delimited by a marked disconformity. 



"U. S. G. S., Bull. No. 210. 



t Eeport N. Y. S. Pal., 1902, p. 996 £f. 



