310 Gardner — Relation of the Late Tertiary Faunas. 



more closely than does the present Gulf Stream, but swung off 

 into the open sea in the vicinity of Hatteras so that its influence 

 upon the Yorktown fauna was almost negligible. 



Differences in depth of water in the areas of the late Miocene 

 and early Pliocene that are now available for study were 

 doubtless very slight, so slight that it is very hazardous to 

 attempt to differentiate their effects upon the faunas. It seems 

 highly probable that the Yorktown, the Duplin, and the 

 Waccamaw, were all of them laid down in water, rarely, if 

 ever, exceeding fifty fathoms in depth, and that the bathy- 

 metric variations were as great within the formations as they 

 were between them. The sea floor was rather certainly more 

 sandy during the Duplin and Waccamaw than it was during 

 the St. Marys and Yorktown, the conspicuous abundance in 

 Virginia and northern North Carolina of such a form as 

 Mulinia congesta Conrad indicating dominantly muddy bot- 

 toms in some portions, at least, of the Chesapeake, while the 

 profuseness of Oliva litter ata Lam. and Olivella mutica Say 

 give evidence of extensive sand flats during the Duplin and 

 Waccamaw. 



There is, then, every reason to believe that already in the 

 late Tertiary, present-day conditions had been approximated 

 along the east coast. The faunas of Virginia and North 

 Carolina flourished in rather shallow, inshore waters, into 

 which mud and sand were being freely carried, the waters of 

 the Yorktown basin being slightly but not much warmer than 

 those off the Virginia coast to-day, while the Duplin and Wac- 

 camaw faunas were obviously in more direct communica- 

 tions with the Floridian life than are the present faunas off 

 Hatteras and Cape Fear and indicate slightly warmer climatic 

 conditions than do those of the Yorktown. 



Johns Hopkins University, 

 Baltimore, Md. 



