170 W. R. Doll— Geology of Florida. 



fresh-water fauna out on .to the shoals, where they died. Part 

 of the bottom became elevated nearly to the surface, oyster 

 banks were formed on it, and thecompacter parts became water- 

 worn. Large tortoises wandered there, and occasional mam- 

 moths. The absence of shells, like Litorina and Nerita, seems 

 to indicate that the dry beaches were sandy rather than rocky. 

 In the course of time elevation so shoaled the water that only 

 species like Venus cancellata and others able to live between 

 tide marks could remain. Finally the area became cut off 

 almost entirely from the sea and occupied more or less by fresh 

 water ponds in which the pond-snails multiplied in myriads. 

 Drifting sand has buried these and in its turn has been covered 

 with a thin coat of humus in which the pine, palmetto, and a 

 host of scrubby plants make a fairly successful fight against the 

 progress of civilization. 



The history of Ballast Point seems to have been much the 

 same in Miocene times, except that there the land seems to have 

 risen sufficiently to enable true air-breathing landsnails to 

 flourish. On the Caloosahatchie they are extremely rare, only 

 one or two specimens having turned up among thousands of 

 fresh-water snails. On the other hand, if Ballast Point rose 

 higher, it was afterward depressed lower, so that several feet of 

 marine orbitolite rock could be formed over it. On the Caloo- 

 sahatchie the thickness of the marine strata over laj^ers of the 

 fresh water limestone did not exceed six inches. 



As it ma} 7 be supposed that the admixture of fresh water 

 forms with the marine forms has been due to mechanical mix- 

 ture after fossilization, which in certain places where the marl 

 is penetrated by roots from above, might have occurred, I will 

 add in concluding that the same mixture occurs in the interior 

 of the most flinty chert bowlders. It is curiousl}'' paralleled by 

 the mixture I have found in shells collected by the IT. S. Fish 

 Commission, in some of the inner lagoons of the Bahamas, 

 where a similar series of geological changes maj^ be supposed to 

 be at this moment in progress. Among the fresh water species 

 is a large Cyrenella, a genus recently found by Hemphill in a 

 living state in a South Florida marsh. It has not been before 

 known from the United States, and was originally described 

 from Senegal. 



No coral rock or coral reef formation was anywhere observed. 

 The coral-formation observed by Agassiz in the region in the 

 Re}'s, must be of very limited scope, as it has not been report- 

 ed from the mainland of Florida by any modern geologist. 

 That the peninsula could not have been formed on the 

 Agassizian hypothesis was pointed out by me in 1882. 

 (Saturday lectures, No. 7, p. 18 ; Washington, Judd and Det- 

 weiler, 1882.) 



