SOME FLORIDA' LAKES AND LAKE BASINS. 49 
of the state. On the contrary they are on the uplands, and occur 
in sections having a hilly or rolling topography. Sinks or open¬ 
ings occur through which the water escapes into the underlying 
formations. These sinks are located ordinarily at the foot of a 
steep bluff bordering the lake. Around the main sink one finds 
ordinarily other sinks of more recent formation indicating the man¬ 
ner and direction, of enlargement of the basin. The sinks through 
which the water escapes are variable in depth but reach in all cases 
to underlying limestones. A channel as a rule leads back from this 
sink across the lake bottom representing the main channel of flow of 
vater to the sink. Aside from this channel the bottom of the lake is 
relatively flat and level, although slight local depressions occur 
involving in some instances differences of level, of ten to fifteen 
feet. The soil in the lake basins varies considerably. In some 
of the lakes—those which seldom go dry—there is an accumulation 
of muck or peat formed largely from pond lilies and other aquatic 
vegetation. Local depressions in the lake often have an accumu¬ 
lation of this material amounting to several feet. Some of the other 
lakes which frequently go dry have little or no muck except in de¬ 
pressions which hold water even in dry seasons. Beneath the 
muck is usually found light colored sand washed and blown from 
the neighboring highlands. This sand may be several feet deep in 
places, elsewhere it is largely absent. Ordinarily a sandy clay 
occurs beneath the sand. 
When these lakes dry up the water is commonly reported as 
running out very suddenly. This, however, is usually not the case. 
As long as the lake has sufficient water to cover the entire basin 
the lowering of the water surface proceeds very slowly. Subse¬ 
quently when the total surface area of the lake becomes much re¬ 
stricted the lowering of the water surface, proceeds much more 
rapidly. This leads to the statement that the water of the lake dis¬ 
appeared suddenly while as a matter of fact in many cases the 
water escapes through the sink no 1 faster and indeed hardly so 
fast during the dry season as it had been escaping when the lake 
was full during the season of normal rainfall. It is true, however, 
that new sinks occasionally form in the bottom of the lake. In 
the case of the formation of new sinks the rate of escape of the 
water is increased. 
ORIGIN AND HISTORY OF DEVELOPMENT. 
The origin of these lake basins is a part of the history of de¬ 
velopment of the general topography of the region. In this de¬ 
velopment both mechanical erosion and erosion by solution have 
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