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 measurements 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 Floridai hammock belt.
Both kinds of lakes fluctuate perhaps a foot or so with the seasons, 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)
fThe vegetation in and around the small lakes-"is., usually arrangedI in more or less perfect concentric zones, corresponding to0 the depth of the water, or the distance above it on the shore. The boundaries between them are very ill-de~fined, 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 coffeecolored water-to shut off the sun's light entirely, and all flowering plants, ferns, mosses, etc., need light to grow., In the depths of