FREE INSTITUTE OF SCIENCE 



1549 



TERTIARY FAUNA OF FLORIDA 



lead various geologists to the conclusion that a continuous coast or belt of 

 islands must have extended from the Mediterranean region to the Antilles. 

 The thickness and extent of the Vicksburg limestone, stretching from the 

 Floridian region to Costa Rica, and its singular absence from the Antilles, so 

 far as yet identified, taken together with the comparative thinness of the post- 

 nummulitic Oligocene on the Gulf coast and its enormous development in the 

 Antillean region, the north shore of South America, and the region of Middle 

 America south of Mexico, suggest that during the period indicated there was 

 at first a depression of the continental border coincident with elevation of An- 

 tillean lands, while during the period of the tipper Oligocene these conditions 

 were reversed, the continental sea margin being brought near to, and even, at 

 the Ocala Islands, above the surface of the sea, while a depression of Antillean 

 lands and Middle America permitted the formation of those great bodies of 

 marine limestones and marls for which the upper Oligocene of those regions 

 is so remarkable. As in Europe so in America, lake-beds were formed away 

 from the seacoast, where the bones of Oligocene vertebrates were entombed to 

 serve in the future as convincing evidence of contemporaneous evolution. Again, 

 as in Europe, those changes which elevated the Alps terminated the processes 

 assigned to Oligocene time ; so in America the Middle American highlands, 

 the larger Antillean islands, and the peninsular island of Florida were up- 

 lifted, the two Americas united, and vast physical changes consummated. Coin- 

 cidently at the north the boreal coasts were gently depressed and the waters of 

 the Miocene sea extended over the ruins of the Oligocene forests. 



As indicated by the changes in the fauna, the physical changes attending 

 the close of the Oligocene were at first slow, allowing a certain element of 

 transition to appear in the Oak Grove or uppermost Oligocene fauna. At the 

 last they appear to have been sudden, at least the change in the fauna on the 

 Gulf coast was absolute and complete. The change was not only in the species 

 and prevalent genera of the fauna, but a change from a subtropical to a cool 

 temperate association of animals. Previously, since the beginning of the 

 Eocene, on the Gulf coast the assemblage of genera in the successive faunas 

 uniformly indicates a warm or subtropical temperature of water, and the sedi- 

 ments uniformly show, from the Jacksonian upward, a yellowish tinge due to 

 oxidation. In the Oak Grove sands come the first indications of a change 

 towards the gray of the Miocene marls. With the incursion of the colder 

 water the change becomes complete. Not only do northern animals compose 

 the fauna, but the southern ones are driven out, some of them surviving in 

 the Antilles to return later. Some change along the northern coast permitted 



