118 FLORIDA GEOLOGICAL SURVEY— 15 TH ANNUAL REPORT 
are practically nil. The source of the material forming the clays and 
other sediments must be sought elsewhere. 
During the Eocene and Oligocene periods the sediments were 
marine, representing shallow-water deposition and were formed prob¬ 
ably while all of Florida and the coastal plain sections of Georgia and 
Alabama were yet submerged. These formations were deposited under 
conditions which were uniform over wide areas. 
The Floridian peninsula partially emerged from the sea early 
in the Miocene period. Erosional forces set at once to rework and alter 
the configuration of the then existing surface. Solution of the under¬ 
lying limestones and the resultant formation of sinks also began about 
this time, affording depressions for the accummulation of lacustrine 
deposits. Thus conditions very similar to those existing today began 
and have continued with but little change to the present time. 
As deposits of transported clay may differ in thickness, character, 
and extent, according as the material has been deposited in flood-plains, 
lakes, swamps, estuaries or the open sea, corresponding variations are 
found in the Florida clays. Clays deposited in the shallow sea or tidal 
marshes are usually widespread and more uniform. Thus the Chatta¬ 
hoochee, Tampa and Choctawhatchee clays are fairly uniform over the 
areas they occupy. Under fluviatile and lacustrine conditions, on the 
other hand, variations in current and variations in the amount and 
character of the sediments carried resulting from erosional and climatic 
conditions, cause deposits of these types to differ widely in character. 
Thus the Alum Bluff, Citronelle and many Pleistocene deposits display 
marked irregularities. 
The subsequent erosion and reworking of formations already de¬ 
posited has been an important process in Florida. This accounts for the 
numerous isolated remnants or outliers of formations to be found in 
the State. The sedimentary kaolin deposits are an example of this 
condition. It also accounts for the presence of one distinct kind of 
material in two or more formations. Thus phosphatic material has been 
derived from the Alum Bluff formation, sorted and concentrated in later 
deposits to such an extent as to make mining profitable. This is also the 
origin of the Bartow clay. 
The clays of Florida were derived either directly or indirectly 
from the crystalline rocks of the southern Appalachians exposed in Ten¬ 
nessee, North and South Carolina, northern Georgia and Alabama. 
