162 W. H. Ball— Geology of Florida. 



In referring to the age of the deposits, while the old terms 

 Miocene, Pliocene, etc., may be used for the sake of conven- 

 ience, it must be clearly understood that, as at present denned, 

 they are only of relative value and indicative at most of strati- 

 graphical succession in a very limited sense. As determined by 

 their invertebrate fauna, the Pliocene, for instance, of South 

 Europe, is probably older than the strata called Pliocene in 

 America, at all events, it is highly improbable that they repre- 

 sent synchronous geological epochs. The method of determin- 

 ing which name should be used for a particular division of the 

 Tertiary, by taking percentages of the supposed extinct species, 

 is, on the face of it, impracticable, illogical and misleading. 

 Our knowledge of the Tertiary in America is still so fragmen- 

 tary and imperfect as to render a sychronic sub-division of all 

 the Post-Cretaceous strata impossible for the present. 



Contemporaneous formations. 



A large part of Southwestern Florida is covered with a sandy 

 stratum which may average between two and five feet in thick- 

 ness and has its upper surface more or less mixed with, or con- 

 cealed by, the superficial humus. Although in the northern 

 part of the State, ridges marking former boundaries of large 

 lakes rise to more than two hundred feet above the sea, in the 

 southern part the highest elevation is much less, and I have 

 been informed that the rim separating Lake Okeechobee from 

 the lowlands stretching to the Gulf of Mexico, was found by 

 the Canal Company's engineers to be only some twenty feet 

 high, a large part of which is composed of peaty vegetable 

 matter. In the section afforded by the river below Port 

 Thompson and between it and the Gulf, nothing over fifteen 

 feet in height was observed by us, though the land may rise 

 somewhat higher, away from the river. A large part of the 

 sand is derived from the wear of the limestone rocks which are 

 webbed and clotted with bands, strings and irregular masses of 

 silica, from the Miocene up, and over much of the State, though 

 very irregularly distributed. But on the shores of the Gulf 

 among the purer siliceous sand I observed that there are als.o 

 particles of crystalline rocks foreign to the region and which 

 occasionally are found in pieces weighing several ounces. The 

 distribution of these particles and pebbles seems too general to 

 permit of referring them to casual discharges of ballast by 

 vessels. 



The process of rock-formation is going on in a more obvious 

 manner than would be expected along the Gulf shores of West 

 Florida. There is a general opinion among the inhabitants, 

 which was frequently expressed to me, in conversation, to the 



