Tertiary Mollusks of Florida. 



BY W. H. DALL. 



PART II. 



INTRODUCTORY. 



On the Marine Pliocene Beds of the Carohnas. 



la discussing the fine Pliocene fauna of the Caloosahatchie, it has been 

 necessary to consider the other American faunas supposed to be of the same 

 age or which have been referred by various authors to the same geological 

 epoch. Omitting the beds of this age south of the Rio Grande and in the 

 Antilles, and exclusive of the Pliocene beds of the Pacific Coast, the Caloosa- 

 hatchie beds are the only marine Pliocene deposits of the United States of 

 which the geological age has been admitted without controversy since they 

 were first described. They were stated by Professor Heilprin,' in his orig- 

 inal paper, to " give us the first unequivocal evidences of the existence of a 

 marine Pliocene formation in the United States east of the Pacific slope," and 

 therefore may fairly be regarded as constituting for this country the standard 

 by which other beds, for which a similar age is claimed, should be tested. 



In the earlier publications on geology and paleontology which were 

 made in this country, the word Pliocene was used to cover the Tertiary forma- 

 tions subsequent to the Eocene, and the use of the word Miocene was of later 

 date. After the nomenclature of the Tertiary, as at present understood, had 

 been accepted by American geologists, the application of these terms became 

 a subject of some difference of opinion, owing to imperfect kriowledge of the 

 faunas and the different points from which the subject was viewed by geolo- 

 gists. In general, the percentage of living forms contained in the beds, after 

 the method of Deshayes and Lyell, was taken as decisive of the place the 

 horizon should occupy in the scale of the Tertiary. 



The area where marine Pliocene might be expected to occur is bounded 

 on the north by part of Virginia, and extends southward along the coast to 

 the peninsula of South Florida. 



Portions of the Tertiary belt along this coast have been subjected to 

 considerable chan^^es of level, denudation, and obscuration by the accumulation 

 of Pleistocene sands. Over much of the rest the Post-Eocene beds lie uncon- 

 solidated in the form of marl or shelly gravel, little elevated above the sea or 

 the flood-line of the rivers which cross it on their way to the ocean. In an 



■ These Transactions, Vol. I., p. 64 B. 



