52 
FLORIDA GEOLOGICAL SURVEY—THIRD ANNUAL REPORT. 
limestone, an average specific gravity of 2.5, a layer one foot thick 
over one square mile should weigh about two and one-sixth million 
tons. The calculated rate of removal of this rock is about four 
hundred tons pej* square mile per year. From these estimates it 
would appear that the surface level of the central peninsular sec¬ 
tion of Florida is being lowered by solution at the rate of a foot in 
five or six thousand years. 
With due allowance for a wide margin of error in the above 
estimates it is still evident that a very great amount of mineral 
solids is being removed annually in solution. The first effect of 
solution in limestone is to develop cavities through the rock along 
the line of ready flow of underground water. These cavities grad¬ 
ually enlarge until the overlying material, no longer able to support 
its own weight, caves in, forming a sink. 
The formation of a sink is a first step in the development of the 
many basins large and small occupied by these temporary lakes. 
A sink usually retains connection with the underlying limestone 
for some time after its formation and water entering the sink 
escapes into the limestone. Under these circumstances more or 
less of the material lying immediately around the sink is carried 
by surface wash through the sink. Moreover the large amount of 
water entering through the sink results in rapid solution in the 
limestone of that immediate vicinity. The result is frequently the 
formation of other sinks in close proximity to the first. As old 
sinks become clogged or partly filled, new sinks form by this pro¬ 
cess continually enlarging the basin. 
Not infrequently a sink forms in or near the bed of a stream. 
When this occurs the lower course of the stream, or a part of it, 
may be reversed. Where many sinks form in succession or through 
a long period of time the valley of the stream is thereby enlarged 
and is frequently carried to a level lower than the original outlet. 
Lakes Iamonia and Lafayette in Leon County and Alachua Lake in 
Alachua County are illustrations of basins of this type. 
RELATION OF THE LAKE BASINS TO THE LEVEL OF 
PERMANENT UNDERGROUND WATER. 
It is important to note the relation of thes^ lake basins to the 
permanent underground water level of the formation into which 
they drain. It is a well established fact that solution by undei- 
