158 FLORIDA GEOLOGICAL SURVEY SIXTH ANNUAL REPORT. 



iially lowered. This gradual change in the water line in geologic 

 time affects the life history of the lake basins, but does not of course 

 affect the observed behavior of the lakes. 



SUMMARY, 



The basins of the temporary lakes have their origin in erosion 

 by solution and by mechanical wash. Some of them appear to 

 represent the enlarged valleys of what was originally a small 

 stream. Sinks form along these streams diverting the course of 

 the water into the underlying limestones. Other basins originate 

 fromi sinks in no way connected with stream valleys. The origin 

 of the sink was due primarily to solution in the limestone. After 

 the sink is formed the general level of the surrounding area is low- 

 ered somewhat by mechanical wash, the material being carried into 

 tlic sink. Subsequently other sinks form in the immediate vicinity, 

 due also to solution. The large amount of water which entered 

 the limestone from the sinks already formed facilitates solution 

 and results in the formation of additional sinks. The continuance 

 of this process through a long period of time results in the develop- 

 ment of the large basins occupied by these lakes. From their manner 

 of development it follows that the steepest bluffs as a rule are those 

 immediately facing the active sinks. Likewise for reasons already 

 given new sinks occur most frequentlv in the area immediately sur- 

 rounding the active sink. The lakes occupy basins that have worked 

 their way through the surface deposits, chiefly the Alum Bluff for- 

 mation, down to or nearly to the underlying limestones of either the 

 Chattahoochee or the Vicksbursf formations In anv case, however, 

 tlie lake basins can scarcelv be lowered below ground water level, 

 since for a stream entering a sink, the permanent ground water level 

 is base level. 



The behavior of the lakes is largelv explained by the seasonal 

 and periodic variation in the rainfall which affects the ground water 

 level. The lakes appear to go dry suddenly. This, however, is often 

 more apparent than real. So long as the entire basin is submerged, 

 the water line recedes so slowly as scarcely to be noticed. After- 

 wards, however, when only a part of the basin is covered, or when 

 there is water only in the small basin immediately around the sink, 

 the water lowers very rapidly and the lake seems to be suddenly run- 

 ning dry. It is true, however, that the escape of the water is not 

 infrequently facilitated by the formation at low water stages of new 

 sinks. 



It is doubtless true that some of the lakes, especially the 



