GIRTY, GEOLOGIC AGE OF THE BEDFORD SHALE 309 



defined and the real question is whether as such, from all the evidence 

 at hand, it belongs more properly with the one system or with the other. 



The base of the Carboniferous system in this country, as usually recog- 

 nized, is the Kinderhook group of the Mississippi Valley; similarly the 

 top of the Devonian system is the Chemung group of New York. Now, 

 there is substantial evidence for believing that the Berea sandstone repre- 

 sents about the horizon of the Kinderhook and that it occurs several 

 nundred feet above the top of the true Chemung. The evidence for this 

 may be briefly summarized as follows : The representative of the Berea 

 in Crawford and Erie counties in northwestern Pennsylvania appears to 

 be the "Corry" sandstone. The "Corry" is more fossiliferous than the 

 Berea and contains a varied and characteristic fauna. The "Corry" 

 horizon carrying this fauna can be traced eastward to Cobhams Hill just 

 east of Warren, where it comes in immediately above what has been called 

 the "sub-Olean conglomerate" (Knapp formation), in the short interval 

 which separates that formation and the Olean conglomerate. Beyond 

 this the "Corry" horizon cannot be recognized, but it seems to be a mat- 

 ter of common agreement 14 that the "sub-Olean conglomerate" at Warren 

 and the beds beneath represent the formations which in the Olean quad- 

 rangle come in below the Olean conglomerate, where an interval of about 

 500 feet, comprising the Oswayo and Cattaraugus formations, occurs 

 above the typical Chemung. Similar facts are indicated by I. C. White's 

 work in Crawford and Erie counties, 15 since he recognizes the Venango oil 

 sand group (which he calls Upper Chemung), with a thickness of 310 

 feet, and the Biceville shale with a thickness of 80 feet as intervening 

 between the Chemung proper and the formations for which he used 

 the names Corry and Cussewago. However many errors in detail there 

 may be in these tracings and correlations, it seems safe to conclude that 

 an interval of 400 or 500 feet does intervene between the top of the true 

 Chemung and the "Corry" (Berea) sandstone in this area, which is prob- 

 ably represented in Ohio by the Bedford, Cleveland and Chagrin forma- 

 tions. 



The first point to be considered in the paleontologic aspect of the 

 problem is the affinity of the Bedford fauna, its predominant Devonian 

 or Carboniferous facies interpreted on the facts of the general region in 

 which the Bedford shale and the Bedford fauna were developed. 



Many genera and a few species, after a greater or less development in 

 the Devonian, pass upward into the Carboniferous, ranging to various 

 horizons in the Mississippian or even above. In most cases, there is no 



14 See the report by Glenn, Butts and Clarke already cited. 



15 Sec. Geol. Surv. Pennsylvania. Rept. Q. 4, 1881. 



