W. H. Ball— Geology of Florida. 169 



not uncommon. The intermixture of fresh water shells and 

 marine ones, is characteristic of the whole deposit, though the 

 upper stratum contains proportionally many more fresh-water 

 individuals. At the canal, and for some distance below, the 

 beds above described are capped by a very hard Quaternary 

 limestone full of silex and containing only fresh-water shells 

 though occasional intercalated thin layers of marine shells, 

 covered again by fresh water deposits, show that the sea was 

 not far off, and that small alternations of level probably 

 occurred. The same compact limestone, with the same species 

 of Planurhis, etc., occurs near Hillsborough, by Tampa, and 

 has been dredged in large masses from the channel by which 

 the harbor of Tampa is entered. This shows a very wide 

 extension of this deposit, the two localities being some ninety 

 miles apart in a direct line. 



The marls of the Caloosahatchie contain a large number of 

 species, of which a fair proportion, perhaps one-tenth, are sup- 

 posed to be extinct ; many of the others are known only from 

 deep water. How many of the so-called extinct ones, like 

 Amusium Morioni, will turn out to be still living when the 

 deeper waters of the Floridian coast are thoroughly dredged 

 remains to be seen. A number of the species appear to be 

 more nearly related to shells known from the Asiatic or 

 Californian coasts of the Pacific than to the shells of adjacent 

 waters. But these apparent relations depend a good deal on 

 our ignorance of what the deep waters of the Gruff really con- 

 tain. In their curious partial silicification these beds afford an 

 interesting parallel to those of Ballast Point, and show that 

 similar chemical action has been going on since Miocene times 

 on this coast. 



The age of the Caloosahatchie beds is much the same as 

 others which have been called Pliocene on our Eastern coast. 

 The time has not yet arrived, nor is our knowledge of any part 

 of our later Tertiaries sufficient to enable us to decide finally as 

 to their chronologic relation to each other ; except in the most 

 tentative way. But without reference to their place in the 

 system, the geological history of the Caloosahatchie marls is 

 clearly stated in their structure. 



The assemblage of species on the whole, in the principal 

 stratum, is such as one might expect to find in water from 

 twenty to fifty feet in depth, judging by what we know of 

 living mollusks. Mixed with these are a certain number of 

 shallow-water forms which may be supposed to have flourished 

 as the water became shoal by elevation of the sea bottom. 

 There were lagoons of fresh water and probably short streams 

 emptying into the sea, and in time of flood sweeping their 



