166 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 covering 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 10 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, several being simply wide places in the St. John's and Kissimmee Rivers.
 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-hole's 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 110w than they were a generation o so ago, as shown by the encroachment of young long-leaf pines ov their shores.* This may be due to a permanent lowering of the ground-water level by numerous flowingr artesian wells bored at lower elevations, but the matter has not been sufficiently investigated.

 *See 3d Annual Report, p. 266.