SOME FLORIDA LAKES AND LAKE BASINS. 121 



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 

 sttep 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 

 water 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- 

 ktion 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 oc- 

 curs beneath the sand. 



When these lakes dry up the water is commonly reported as 

 nmning 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 faster and indeed hardly so 

 fast during the dry season as it had been escapmg when the lake 

 was full during the season of normal rainfall. It is true, however, 

 that new sinks occasionaly 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 



