126 FLORIDA GEOLOGICAL SURVEY-SEVENTH ANNUAL REPORT. 
GEOLOGY. 
The geologic structure in central Florida is not complicated, the 
formations being of sedimentary, or sedimentary-organic origin, 
and but little disturbed from their original horizontal position. Over 
a considerable part of the area described in this report the Ocala 
limestone is the country rock.* This formation, the type locality of 
which is at Ocala, has been fully described and its general distribu¬ 
tion mapped in the preceding reports of the Survey. The formation 
consists chiefly of a light-colored, granular, highly fossiliferous lime¬ 
stone. As a rule the rock when taken from the pit is soft, although 
it hardens upon exposure. Locally, however, the limestone has be¬ 
come compact and more or less crystalized, it also' contains masses 
and layers of flint. 
Overlying the Ocala limestone is found remnants of upper Oli- 
gocene deposits, particularly of the Alum Bluff formation which 
includes calcareous and phosphatic sands and sandstone alternating 
with sandy clays and beds of fuller’s earth. These later deposits, 
although formerly extending over the whole area, are now found 
only on the uplands or capping the hills, having been largely re¬ 
moved elsewhere by erosion. 
The residue of these formations was reaccumulated, probably 
during Pliocene time, to form the Alachua formation, in which is 
found the hard rock phosphate deposits. The formation of these 
deposits and the processes by which the hard rock phosphates accu¬ 
mulated have been fully described in the preceding reports of the 
State Survey. Local Pleistocene or later deposits are found in this 
part of the State in caves and in crevices in the rock as well as in 
lake basins and in sinks. 
Since becoming dry land this area has been very profoundly 
modified by surface and underground erosion. Not only has the 
surface configuration been modified, but new drainage conditions 
have been established which in turn affect both the soils and the 
vegetation. 
*The general term Vicksburg Limestone has usually been applied to this 
formation, and is so used in the Soil Survey report on this area. Recent in¬ 
vestigations, however, seem to indicate that the Ocala Limestone is to be rec¬ 
ognized as a formation distinct from the Vicksburg and referred to the upper 
Eocene. See report on Pebble Phosphates (this volume). 
