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FLORIDA STATE GEOLOGICAL SURVEY. 
RECENT. 
The establishing of sharply marked limits for geologic time in¬ 
tervals is a difficult task, particularly in regions where there are no 
well-marked breaks in the stratigraphic succession nor sudden changes 
in the character of the fossil evidence. While there may be differences 
of opinion as to where the line between Recent and Pleistocene time, 
as applied to the geology of southern Florida, should be drawn, the 
writer includes as Recent all deposits that are being laid down or have 
been laid down since the last well-marked change in elevation of the 
land surface. 
Most of the Recent deposits are unconsolidated; they include peat, 
marl and sand. The consolidated rocks embrace coquina, a few de¬ 
posits of beach rock of no special importance, some of the mass of 
calcareous material made up of bits of corals, coralline algae, shells and 
other organic remains now hardening on the Tortugas; the growing 
coral reef outside the keys; worm rock and oyster banks. 
PEAT. 
Surficial deposits of peat are found throughout the Everglades 
where saw-grass grows tall and in places outside the main body of the 
.saw-grass. They have resulted from the subaqueous, incomplete, de¬ 
cay of roots and blades of saw-grass and other swamp vegetation. The 
thickness of the peat varies greatly. In places the peat rests on rock ; 
in places, especially toward the southern edge of the Everglades on 
marl; over considerable areas, as at New River, it rests on sand. 
The average rapidity with which peat is now accumulating in the 
'Glades is unknown, as is the rate of increase under the most favorable 
or most unfavorable circumstances. Hence the thickness of a peat 
bed at a particular place can not be used as a measure of the time that 
has elapsed since peat formation began there. 
MARLS. 
These include beach, swamp, lagoon and sea bottom deposits of 
finely divided calcareous material, differing in appearance, origin and 
manner of deposition. Some represent the rock, shell, or coral flour, 
ground up by the mill of the surf; some, as those accumulating in 
places in the Everglades and in pools along the coast of the mainland 
or the keys, represent lime that had been dissolved and later precip¬ 
itated through the evaporation of the water that held it in solution, 
while other deposits, such as the marls accumulating on the bottom of 
Whitewater Bay, have been precipitated from solution in ways not 
clearly understood. From the first and third of these classes of marls 
have been formed the limy oozes that cover wide expanses of the bot¬ 
tom of the Bay of Florida, the inlets of the mainland, and the pas- 
