W. A. Verwiebe — Berea Formation. 53 



feet.* The same is true of the Claysville,f and the Burgetts- 

 town and Carnegie quadrangles.:}: In the Claysville quadran- 

 gle the author (M. J. Munn) evidently realizes that there is a 

 discrepancy somewhere and tries to explain it in the following 

 words : " The writer does not question the correlation by Butts 

 for northern Pennsylvania, but, in tracing the Hundred-foot 

 sand southward to Washington county from Clarion, there is 

 evidence that the sand is broken by persistent shale beds into a 

 group of sandstones embracing the Fifty-foot, the Gantz and 

 the Murrysville or Butler Thirty-foot sands, and that the last 

 sand is equivalent to the thin oil-bearing sand in southeastern 

 Ohio, which is widely known as the Berea sand."§ Thus he 

 clearly defines the position of the " Berea sand " of Ohio, but 

 not the Berea sandstone of northern Ohio, for he includes in it 

 all the rocks down to the base of the Venango 1st oil sand ; 

 and concludes : " If this is true, the Berea sand of southern 

 Ohio is equivalent to only the upper portion of the Berea of 

 northern Ohio." On the basis of the above correlation the 

 Pocono is made to include all rocks between the top of the 

 Burgoon and the base of the Hundred-foot. 



This tendency to fix the lower limit of the Pocono at the 

 base of the Berea or its equivalent is no doubt an excellent one. 

 Although the evidence of a disconformity is perhaps not as 

 striking or apparent as in the case of the other systems, yet it 

 certainly occurs locally. Furthermore, the paleontologic evi- 

 dence is sufficiently convincing to indicate a probable break. 

 At any rate it is granted by some of our most eminent authori- 

 ties! that the base of the Berea certainly forms the most con- 

 venient place to draw the line between the Devonian and the 

 Mississippian systems. Assuming that this is the case, it will 

 immediately be patent to one familiar with the stratigraphy of 

 western Pennsylvania that a great deal of obscurity and uncer- 

 tainty in correlation will be eliminated. It is admitted by all 

 who have worked in the oil fields, that the top of the Devonian 

 is difficult to fix. It seems, therefore, that the proper correla- 

 tion of the Berea sandstone should serve also to fix the base of 

 the Pocono or the Mississippian. This, of course, is not a new 

 idea. It simply became apparent that no sharp dividing line 

 between the systems could be established by tracing the forma- 

 tions from the east, hence they were traced from the west. 



* U. S. Geol. Survey, Folio No. 176, 1911. 



•(•Ibid., No. 180, 1912. 



ilbid., No. 177: also Bull. No. 456, 1911. 



gU. S. Geol. Survey, Bull. No. 456. p. 16, 1911. Also Folio No. 180. 



f Ptosser, C. S., The Huron and Cleveland Shales of Northern Ohio, Jour, 

 of Geol., vol. xxi, p. 362, 1913. Prosser, C. S., Geol, Survey of Ohio, Bull. 

 15, pp. 106 and 512. Girty, G. H., Proc. Wash. Acad. Sci., vol. vii. p. 6, 

 1905. Also see " Geologic Age of the Bedford Shale of Ohio," Ann. of N. 

 Y. Acad. Sci., vol. xxii, p. 295, ff. 



