518 PROCEEDINGS OF THE ACADEMY OF [Sept., 



beds were formed. The order of emergence of the various de- 

 posits — which were all more or less local — may therefore be stated 

 to be: (1) Jackson stage, (2) Red Bluff substage, (3) Byram sub- 

 stage, and (4) Vicksburg stage. The Scohinella ccelata men- 

 tioned by Mr. Langdon among the Byram fossils, is not exactly 

 the same as the form described from Vicksburg under that name, 

 but is a very well-marked variety or subspecies, related, in fact, 

 more closely to the form occurring at Red BlufT. The degenera- 

 tive Vicksburg modification, strangely enough, appears to be 

 entirely wanting in the lower — limestone — horizon, but is suffi- 

 ciently common in the upper marls, as in the case of OrMtoides 

 manteUi alluded to above. 



