DISCUSSION. 



Dr. W. B. Clark : What grounds are there for correlating the beds ex- 

 posed on the Chattahoochee with the Salt mountain beds ? 



Dr. C. A. White : I should like to ask about the correlation of the Eutaw 

 group and the Torabigbee sands, which have been fouud to rest directly upon 

 the equivalent of the Eutaw group ? 



Mr. Langdon : At Eutaw and in the upper part of the micaceous sands 

 at the ferry bluff, casts of nautilii and ammonites as well as shark teeth have 

 been found. Above the calcareous greensand, shark teeth have been found 

 in what is believed to be the equivalent of the Tombigbee sands, seen below 

 the Choctaw bluffs on the Chattahoochee. Here ambiguous fossil remains 

 have been found, mostly casts, showing a great variety of species. 



The Salt Mountain beds have been seen only at their typical locality. I 

 do not regard them as constituting a group, but as coral islands in Tertiary 

 seas. 



Dr. C. A. White: I have found much difficulty in determining the upper 

 delimitation of the Eutaw group of Tuomey and the lower delimitation of 

 the marine upper Cretaceous series, as it is represented in Alabama and 

 Mississippi. The lower part of the Eutaw group seems to be inseparable 

 from the Tuscaloosa group, the strata of both being of non-marine origin. 

 I regard the Tuscaloosa group of the Gulf-border region as equivalent to 

 the Potomac group of the Atlantic-border region, and the marine upper 

 Cretaceous series, which overlies those groups respectively in the two regions, 

 are plainly equivalent. 



It now seems improbable that the Potomac group is newer than the lower 

 part of the lower Cretaceous, and it has even been referred to the Jurassic. 

 In either case it is plain that there is a wide time-hiatus between the Poto- 

 mac group and the lowermost of the marine Cretaceous strata that have been 

 discussed by Mr. Langdon ; and yet the conformity of the upper upon the lower 

 series is usually so exact as to give no physical indication of such a hiatus 

 as I have indicated. 



(606) 



