FREE INSTITUTE OF SCIENCE 



1595 



TERTIARY FAUNA OF FLORIDA ^^"^ 



In Middle America, and to some extent in the Antilles, this epoch was one 

 of profound physical changes. The two continents were united and have 

 never since been effectively separated. The marine Oligocene strata in Costa 

 Rica, according to Gabb, were elevated several thousand feet. 



The general movement in elevation spread more slowly to the north and 

 east. That no marine Chesapeake deposits have been found in the Antilles is 

 to be explained by the suggestion that they too were undergoing elevation at 

 the time, accompanied, as on the mainland, with more or less active volcanic 

 phenomena. That the Florida fauna was not exterminated is evident, for in 

 the succeeding Pliocene a number of the Oligocene exiles reappear, and in some 

 parts of the Antilles they must have continuously existed in the meantime. 



The Suwannee Strait * between the Floridian islands and the Georgian 

 mainland remained open some time longer, while the Jacksonville limestone and 

 the Chesapeake beds of northern Florida were laid down. Before the end of 

 the Miocene, however, this region also submitted to elevation, the Strait was 

 closed, and the Floridian peninsula and probably the entire Floridian plateau 

 were raised above the sea. Later, in the Pliocene, a slight subsidence, and 

 perhaps a slight westward tilting of the peninsula, took place, accompanied by 

 an increase of sea temperatures. The Pleistocene, though far from glacial as 

 at the north, was a period of diminished sea temperatures and moderate eleva- 

 tion without perceptible tilting. The present epoch has witnessed a slight in- 

 crease in sea temperatures and a very slight, probably continuous, elevation of 

 the peninsula amounting in all to only a few feet. These changes took place 

 without marked catastrophic changes or dislocation of the strata, while only a 

 few miles away, in the island of Cuba, orogenic changes of great magnitude, 

 attended with more or less violence, are believed to have occurred. All the 

 circumstances point to a discontinuity between the action of geologic forces in 

 the Antilles and that of the Floridian region, and this appears to have been the 

 rule since Mesozoic times. 



Another feature upon which emphasis should be laid, and which has hardly 

 received the attention it deserves, is the fact that through a large part of the 

 Floridian region the action of meteorological forces on the rocks of Florida has 

 been exercised in the direction of solution rather than denudation. The char- 

 acter of the rocks, so porous, soft, and soluble, is especially adapted to waste 

 through the percolation of water charged, through the decay of the abundant 



* Named by the writer in 1892, and subsequently called by Foerste the Okeefinokee 

 Strait. 



