FREE INSTITUTE OF SCIENCE 



1551 



TERTIARY FAUNA OF FLORIDA 



eating a still warmer sea-temperature inaugurated the Pliocene. During this 

 period a continuance of immigration of subtropical forms, Miocene exiles and 

 newcomers, is notable. These pushed their way northward, one species, at 

 least, reaching Martha's Vineyard. The records of this extension were partly 

 obliterated by the ice-sheet of the Glacial period and, even as far south as the 

 Carolinas, are very fragmentary. The end of the Pliocene is the beginning 

 of the Glacial epoch. The Pleistocene of Florida shows a change for the cooler 

 and an elimination of the most purely tropical forms from the fauna, but noth- 

 ing like the clean sweep at the beginning of the Miocene. The latter is the 

 sharpest and most emphatic faunal change since the Cretaceous on our coasts. 

 With the exception of a few widely distributed and uncharacteristic species 

 the entire molluscan fauna of the north shore of the Gulf was swept awa}- and 

 replaced by a more meagre fauna of a different type. In the face of this revo- 

 lution no proposition to extend the limits of the Miocene farther down the 

 column seems to me defensible. 



The above summary of the changes in the period between the Vicksburg 

 and the Glacial epoch was sketched in all its main outlines in Bulletin 84 of 

 the United States Geological Survey in 1891, and amplified in the introductory 

 remarks to my " Table of Tertiar}' Horizons" in 1895. Subsequent study has 

 only confirmed the views drawn from the earlier work, and, as a whole, the 

 establishment of this general view may be regarded as the most important 

 result of this study of the Tertiary faunas of Florida. A thorough knowledge 

 of the present faunas of the coast is almost essential to enable one to fully 

 recognize the weight of the evidence, but I am convinced that in its main 

 features the above sketch will stand the test of time, even though some amelio- 

 ration may be expected in minor details. 



In some recent papers on the Oligocene and Eocene it has been suggested 

 that the presence or absence of identical species in the Tertiary beds on either 

 side of the Atlantic is an important factor in deciding the correlation of geo- 

 logical horizons. While this is partially true of older geological horizons, after 

 the Mesozoic epoch the faunal characteristics of the shallow-water Mollusca 

 of different regions became rapidly distinctive. Even in the Eocene but two 

 or three species can be claimed as identical on both shores of the Atlantic, and 

 in later periods it would be most unreasonable to demand of subtropical marine 

 invertebrate faunas in widely separated regions that they shall offer a series of 

 identical species on pain of being refused correlation. We cannot ask that they 

 shall do more than present equivalent stages of evolution in relation to pre- 

 ceding and subsequent faunas, or that a no greater number of identical species 



