GIRTY, GEOLOGIC AGE OF THE BEDFORD SHALE 315 



As I have just shown, the fauna of the Bedford shale and the fauna of 

 the oolitic limestone at Glen Park and at Hamburg are in some respects 

 strikingly alike, but, though the resemblances are undoubted, there are 

 also numerous and important differences. The resemblances consist of 

 the presence in both faunas of identical genera and of related species. 

 Identical species, however, are few and not of the first importance. The 

 Delthyris, the Nucleospira, the Macrodon, etc., of the Bedford shale are 

 not the same species as the Delthyris, the Nucleospira. the Macrodon, 

 etc., of the oolite at Glen Park and at Hamburg. Correlation by similar 

 species is certainly much more hazardous and less satisfactory than corre- 

 lation by identical species. Indeed, although we of course know that all 

 these faunas are more recent than the Hamilton, the table compiled by 

 Professor Weller would indicate that the Glen Park fauna is almost as 

 closely related to the Hamilton faunas as it is to that of the Bedford 

 shale and much more closely related to the Hamilton than to the contem- 

 poraneous Chouteau fauna. Eestricted to their own showing, therefore, 

 I believe that a correlation of the Bedford and Glen Park faunas would 

 not be justified, except in a very provisional and tentative manner. 



However that may be, if, instead of considering the two faunas as iso- 

 lated occurrences, we include, as we are forced to do, the faunas asso- 

 ciated or correlated with them — the t}^pical Kinderhook, the Chouteau 

 and the Louisiana faunas of the Mississippi A^alley in the one case, and 

 the "Bradfordian" faunas of Pennsylvania in the other — it seems clear 

 that we have two entirely distinct faunas, the one showing a strongly 

 Carboniferous and the other a strongly Devonian facies, and we cannot 

 conclude that they are contemporaneous expressions of the same faunal 

 zone on any evidence now known. 



The Bedford and Cleveland shales cannot be definitely identified in 

 the "Bradfordian" rocks of northwestern Pennsylvania, either litho- 

 logically or paleontologically, but there is an interval between the Berea 

 ("Corry") sandstone and the Venango oil sand group which seems to 

 correspond in a general way to that represented in Ohio by these forma- 

 tions, and I personally but little doubt that Bedford and Cleveland do 

 correspond to strata in the "Bradfordian." Even, .however, if they do 

 not, and the "Bradfordian" with its strongly Devonian fauna does en- 

 tirely underlie the Bedford, I believe that the correlation of the Bedford 

 shale with the oolites at Hamburg and Glen Park would not be justified 

 at present. 



The small number of identical species and the almost complete ab- 

 sence of all those characteristic Carboniferous types which by Professor 

 Weller's correlations occur at the same horizon as the oolitic limestones 



