INSTITUTE OF SCIENCE, PHILADELPHIA. 207 



Floi'idian region has contributed greatly toward the apparent success of this 

 attempt. 



The close of the Eocene was marked by a movement in elevation which 

 raised Central Florida as an island above the level of the sea, separated by a 

 wide strait from the continental shore-line of Georgia. At the same time a 

 change of conditions took place by which the character of the fauna was sub- 

 jected to a notable alteration. Nutnimdites and Orbitoides, genera which, had 

 formed until then most conspicuous members of the fauna, together with other 

 foraminifera of smaller size, disappeared entirely, with numerous molluscan 

 genera, and were replaced by others, notably Orbitolites. The fauna was a sub- 

 tropical assemblage similar to that of the Central Antilles, and this continued 

 for a time to be its character. Orogenic changes elsewhere intervened, and, 

 probably by modifying the course of the ocean-currents, affected the character 

 of the Floridian fauna even more profoundly than did those changes which 

 terminated the Eocene. 



The period between the inception of the Miocene and the modification 

 of its original fauna covered the deposition of the beds comprising the 

 Chattahoochee group of Langdon and the Tampa group of Dall, and, from 

 the fact that its warm-water fauna is best displayed in the Chipola beds of 

 Northwest Florida, along the river of the same name, may be called the 

 Chipola epoch. During this epoch subtropical mollusks, such as Cymia and 

 Valuta, flourished as far north as New Jersey. The temperature-indications 

 of the fauna do not differ essentially, as far as our knowledge goes, from those 

 of the previous later Eocene fauna. At no succeeding epoch do we find sub- 

 tropical or tropical mollusks extending northward to such a distance from 

 their present range. If any of the leaf-beds of Greenland are really Miocene, 

 these facts authorize the suspicion that the period when walnuts ripened on 

 the shores of the Arctic Sea may have been synchronous with the warm 

 Chipola epoch of the early Miocene. 



Whether an eastward deflection of the Gulf Stream, connected with 

 elevation of the Great Carolinian Ridge, or some other undetermined cause, 

 offered the opportunity, a colder inshore current seems to have crept south- 

 ward along the continent, penetrated the strait between Georgia and Florida^ 

 and washed the northern shores of the Gulf of Mexico. With it came the 

 cold-water fauna appropriate to its temperature. This fauna began early in 

 the north, nearly the whole mass of the New Jersey, Maryland and Virginia 

 Miocene being of this character. Southward, the mass relative to that of the 

 Chipola epoch gradually diminishes, being less in the Carolinas and least in 

 the Floridian region. With this fauna were introduced the conspicuous forms 

 which are known as characteristic of the Miocene of Maryland and Virginia, 

 the large Pectens and Areas, Venus and Ecphora. Profusely developed about 

 Chesapeake Bay, where it is found in those beds to which Darton and the 

 writer, independently, came to apply the name of Chesapeake, the period in 



