65 



Key West ; Rangia cuneata, Gulf of Mexico to West Florida ; Petri- 

 cola typica, Cape of Florida to the Antilles ; Tritonidia cancellaria, 

 Jupiter Inlet, Florida, to the Isthmus of Darien. These deserve 

 especial notice. Diplodanta soror is common in its occurrence in the 

 Pleistocene of the State ; and Rangia cuneata, as has already been 

 pointed out, is very abundant indeed in the bed underlying Charles- 

 ton. This last-named species, as has already been noticed, is found 

 in abundance in Maryland up the Potomac from Cornfield Harbor. 

 Its occurrence so abundantly so far north as Maryland is very re- 

 markable, and must mean that, at some time during the Pleistocene 

 Period, there was greater warmth in that particular region than to- 

 day, or else that the brackish water has failed in some of the neces- 

 sary conditions to sustain Rangia cuneata. The occurrence of these 

 extreme southern forms, together with the abundance of the two 

 just mentioned and also the Tritonidia cancellaria (on Stono River), 

 almost compel the conclusion that the Pleistocene facies of South 

 Carolina, if different from that of the coast today in the same region, 

 was more southern. 



General Conclusions from the Study of the Tables. — According to 

 Dall, the Pleistocene of Florida shows a change for the cooler from 

 the warm temperature of the Pliocene. He says further : "The 

 Pleistocene [of Florida] , though far from glacial as at the north, 

 was a period of diminished sea temperatures and moderate elevation 

 without perceptible tilting. The present epoch has witnessed a 

 slight increase of sea temperatures and a very slight, probably con- 

 tinuous, elevation amounting in all to only a few feet." McGee may 

 be quoted in this connection : "W. B. Rogers, Sanderson Smith, 

 Cook, Cope, Kerr, Fontaine, Lewis, Chester and others believe it [the 

 Columbia or Pleistocene of the whole coast] was deposited during 

 a period of low temperature." McGee's view also was in accord with 

 this belief. He says that Desor, whose view will be given later, drew 

 his conclusions from too limited data. Conrad, in speaking of the 

 Cornfield Harbor species, says : "Were it not for the presence of 

 Gnathodon cuneatus [Rangia cuneata] , Mytilus hamatus and 

 Area ponderosa, the group would not vary from that now inhab- 

 iting the coast as far north as Massachusetts ; but the occurrence 

 of these three bivalves indicates that a climate equivalent to 

 that of Florida prevailed when the shells of this locality were 

 living in the sea." But this view loses some of its force, since 

 two of the forms he here mentions are known to live at present 

 as far north as Long Island Sound and Cape Cod, namely: 



5— p. d. 



