54 FLORIDA GEOLOGICAL SURVEY-SEVENTH ANNUAL REPORT. 
GEOLOGIC HISTORY OF SOUTHERN FLORIDA. 
If the areal and structural geology has been correctly described, 
the geologic history of southern Florida may be readily interpreted, 
so far at least as it affects the problem of the formation of the phos¬ 
phate deposits. Several periods of deposition are recognized sepa¬ 
rated by more or less well marked intervals of emergence and 
erosion. 
PERIOD OF DEPOSITION OF LATE EOCENE SEDIMENTS 
The Ocala limestone which underlies the Florida peninsula and 
is probably of Eocene age is of marine origin having accumulated 
in sea water of medium depth, and under conditions that were uni¬ 
form over large areas, and for a long period of time.* 
POST-EOCENE PERIOD OF EMERGENCE AND EROSION 
The conditions which permitted the accumulation of the Ocala 
formation continued probably into the Oligocene, and was then fol¬ 
lowed by a period of emergence during'“which the Florida plateau 
was lifted above sea level, becoming dry land. It is difficult to de¬ 
termine the extent of this uplift. That dry land areas existed, how¬ 
ever, is shown by the fact that the top surface of the Ocala limestone 
is irregular having been worn uneven by erosion. Moreover, the 
earliest of the upper Oligocene deposits that accumulated in the vi¬ 
cinity of Tampa contain a very conspicuous element of land and 
fresh water fauna, particularly mollusks,f thus showing that the 
shore line at that time was at no great distance from that locality. 
PERIOD OF DEPOSITION OF UPPER OLIGOCENE SEDIMENTS 
A widespread submergence permitted the extension of the sea 
over large areas during upper Oligocene that for a time had been 
dry land. The deposits that accumulated in Florida at the time of 
this submergence include the Chattahoochee, Tampa and Alum Bluff 
formations, the characteristics and extent of which have already been 
described. The distribution of these formations is such as to leave 
* Vaughan, T. Wayland, A Contribution to the Geologic History of the 
Floridian Plateau, Carnegie Institution of Washington, Publication No. 1 33 , 
pp. 99-185, 1910- 
tDall, W. H., Contribution to the Tartiary fauna of Florida. Wag. Free 
Inst. Sci. Trans. Vol. iii, pp. 3-14, 1890; U. S. Nat. Mus. Bull. 90, pp. 18-19, 1915* 
