MAUYLANU GEOLOGICAL SURVEY Cxlv 



Cape Jlatteras serves as a landmark indicating the mutual boundary 

 between the northern temperate and southern subtropical inoUusk faunas 

 of the present Atlantic coast; aiul it would seem as if in Miocene time a 

 similar arrangement prevailed. 



The upper surface of the Chesapeake in Virginia has been extensively 

 denuded, and the equivalent, if any, of the Duplin beds has been removed 

 over a great portion of the Miocene area. The dip of the remaining 

 deposits, according to Darton, in the northeastern or older portion of the 

 beds, is about ten feet to the mile; in the Nomini section about 7.7 feet 

 to the mile; and in the newest, or Suffolk region, about 6.5 feet to the 

 mile. The beds, as a whole, retain at most about 560 feet of their 

 original thickness. The diatomaceous bed, when present, as is usually 

 the case, lies at the base of the series, on the denuded surface of the 

 Eocene, and if there were earlier deposits which should normally be 

 associated with the Chesapeake, neither in New Jersey nor in Virginia 

 do we find any trace of them remaining. In all cases and throughout 

 its extent the fauna has the characteristics of a shallow-water assembly, 

 without any marked littoral elements, but which might well have existed 

 in the immediate vicinity of low, nearly level, muddy or sandy shores, 

 and have extended off-shore to a distance more or less indefinite, but 

 which did not include any area subject to the influences of an open and 

 unsheltered ocean. 



In Florida we first find, in passing southward from the North Carolina 

 deposits, an extended area of undisturbed and little denuded Chesapeake 

 sediments, and where, as at Alum Bluff on the Chattahoochee river and 

 localities on the Chipola river, they have been carefully examined, they 

 present, with some slight admixture of warmer water forms, a fauna 

 essentially like that of the more northern deposits. Eliminating the 

 species peculiar to the Florida beds alone, of the remainder about forty 

 per cent are common to the Chesapeake of Maryland and fifty-seven 

 per cent common to Florida and North Carolina. Since the northern 

 fauna must have become well established before it could have, as a body, 

 invaded the Florida province with the incursion of cold currents pre- 

 viously described, it is probable that the Alum Bluff Miocene represents 

 in time a period somewhat subsequent to that of the Maryland beds, 

 though in point of evolution of organic life nearly identical. About 



