l66 FLORIDA GEOLOGICAL SURVEY I3TH ANNUAL REPORT 



HYDROGRAPHY. OR DRAINAGE 



Lakes. There is perhaps no essential difference between a lake 

 and a pond, but the former term, in Florida as elsewhere, is usually 

 applied to the larger and more permanent bodies of fresh water. 

 No close estimate of the number of lakes in central Florida has been 

 made, but it is certainly in the thousands. The majority are in the 

 lake region, as might, be expected, but they are common in several 

 other regions, particularly the eastern division of the flatwoods. 

 The largest are Lakes George, Apopka and Kissimmee, each cover- 

 ing something like 100 square miles. The smaller ones, some of 

 which are only a few acres in extent (and not as wide as some 

 parts of the St. John's River) are. approximately circular and have 

 no visible outlets, being merely depressions extending below the 

 ground-water level. But they can hardly be called stagnant,, for the 

 water is doubtless constantly seeping through the sandy soil in the 

 direction of the nearest river. The larger lakes are irregularly 

 shaped and have streams flowing into or out of them, or both, sev- 

 eral being simply wide places in the St. John's and Kissimmee Riv- 

 ers. 



Few soundings have been made in our lakes, but judging from 

 the slope of their shores the deepest may not be over 50 feet deep. 

 As a rule they do not fluctuate more than two or three feet in the 

 course of a year. A few which are connected with sink-holes may 

 be lowered suddenly at long intervals in the manner described 

 by Dr. Sellards in the 3rd and 6th Annual Reports, and those on the 

 St. John's River of course share the fluctuations of that stream, 

 which however are only a few feet. Lake George, being just about 

 the head of tide-water on the St. John's, of course cannot rise much, 

 but Lake Harney, about 200 miles by water from the mouth of 

 the river, is said to have an extreme fluctuation of about seven feet. 



Besides the seasonal variations in level, some of the lakes among 

 the uplands are evidently lower now than they were a generation 01 

 so ago, as shown by the encroachment of young long-leaf pines 01? 

 their shores.* This may be due to a permanent lowering of the 

 ground-water level by numerous flowing artesian wells bored at 

 lower elevations, but the matter has not been sufficiently investi- 

 gated. 



*See 3d Annual Report, p. 266. 



