266 FLORIDA GEOLOGICAL SURVEY—THIRD ANNUAL REPORT. 
PERMANENT OPEN WATER. 
We now come to the most important class of peat deposits, 
namely, those associated with permanent lakes. The lakes of the 
lake region can be divided somewhat arbitrarily into two classes, 
small and large. Most of the small lakes are less than half a mile 
in diameter, approximately circular, with sandy bottoms and no 
outlets; and on account of their small size they never have large 
waves on them. The large lakes are a mile or more in diameter, 
irregularly shaped, and usually connected with streams, and in many 
cases the vegetation around them seems to indicate a slight influence 
of limestone either in soil or water or both. Very few measure¬ 
ments of the depth of these lakes have been made, but the slope of 
the surrounding pine hills seems to continue some distance below the 
surface without much change, instead of red hills passing abruptly 
into flat lake-bottoms as in the prairie-like lakes of the Middle Flor¬ 
ida hammock belt. 
Both kinds of lakes fluctuate perhaps a foot or so with the sea¬ 
sons, and their level varies also from one year to another, probably 
with variations in the annual rainfall. Just at present most of the 
lakes seem to be a few feet lower than they were a decade or 
two ago, for many of the smaller ones have a fringe of saplings of 
long-leaf pine (a tree which demands dry soil) around them, a 
little below what was evidently once high-water mark. (See 
plate 24.1.) 
SMALL LAKES. 
(plate 24) 
The vegetation in and around the small lakes is usually arranged 
in more or less perfect concentric zones, corresponding to the depth 
of the water, or the distance above it on the shore. The boundaries 
between them are very ill-defined, however, for there seems to be in 
most cases a complete gradation from the bonnets, etc., in deep 
water to the pines around the shores. 
The maximum depth at which vegetation can grow in our lakes 
has not been investigated, but it does not take many feet of coffee- 
colored water to shut off the sun’s light entirely, and all flowering 
plants, ferns, mosses, etc., need light to grow., In the depths of 
the lakes there may be algae, diatoms, bacteria, and other low forms 
of plant life, but plants which send up green leaves to the surface do 
not usually grow in more than five or six feet of water. 
In the middle of lakes which do not exceed this depth, or around 
the edges of open water in the deeper ones, one or both of two 
