157 



Midway Stage 43 



Mr. Orville A. Derby, a former Cornellian, now State Geolo- 

 gist of Sao Paulo, in reply to recent inquiries, says:— 



"Your letter of Jan. 28th [1896] has interested me very much. 



"Some years ago while I was still in the Museum, a German 

 paleontologist (whose name I do not now remember with certainty 

 but I think it was Koken) wrote to the Director in the same 

 sense. I replied to the letter calling attention to the more pro- 

 nounced Cretaceous character of the Sergipe fauna and suggesting 

 that he discuss this question for which I offered to furnish the 

 material, but I heard nothing further in the matter. 



" I believe also that some of the German notices of Dr. White's 

 work referred to the Tertiary aspect of many of the fossils , but as 

 far as I know no proper discussion has been given to the subject. 



' ' The age determination of these faunas on geological grounds 

 is weak and would not stand against decided paleontological 

 evidence. The assumption that the different basins are substan- 

 tially of the same age is unproven. We had fallen into the habit 

 of calling all the slightly disturbed fossiliferous beds Cretaceous, 

 and the undisturbed nonfossiliferous ones Tertiary, but without 

 definite proof. 



' ' I had expected that the study of the fossils would show a 

 closer relationship between the faunas than it did. That of Maria 

 Farinha can only be connected with that of Sergipe, which as I 

 understand is the most typical Cretaceous, through that of Para. 

 And if this argument fails its reference to the Cretaceous falls to 

 ground." 



Variation of faunas. 



It seems indeed remarkable that certain very characteristic 

 species of the Midway fauna, throughout Texas, Alabama, Ten- 

 nessee, Mississippi and western Alabama, should die out or be 

 replaced by others between central Alabama and Chattahoo- 

 chee river. There are, to be sure, a sufficient number of connect- 

 ing links in the lower and middle portions of the stage to serve 

 well for correlation purposes. In fact the fauna from the Muddy 

 Creek limestone, Tenn., and that of the basal Eocene beds on the 

 Chattahoochee are remarkably alike. There are, too, the charac- 

 teristic central Midway species of OstrcB, TurritellcB, Venericardice , 

 etc., on the Chattahoochee. But the paucity of Vohitilithes, 

 Crassatella, Cucullcsa, Pseudoliva, et al., is noticeable. The upper 

 Midway bed at the base of the bluff at Ft. Gaines bears a fauna 

 almost wholly new. Its correlation with upper Midway faunas 

 farther west on the Alabama river and near Oak Hill is not 

 proven. We are led to believe that it differs so widely from the 

 last mentioned faunas because of differences in environment; 



