94 FLORIDA GEOLOGICAL SURVEY-THIRD ANNUAL REPORT.

The typical lakes of the lake region are more or less circular in outline, have sandy and often steep sloping sides with no limestone rock exposed at the surface, and having no evident subterranean outlet. Their origin is doubtless due to solutioii, although owing to the considerable thickness of other formations the limestone is seldom observed. After the formation of the lake basin the accumulation of sands and clays has effectively concealed whatever limestones may have been exposed by the original subsidcnce. Any subterranean outlet that may have existed has likewise become clogged in the same way. Typical lakes of the lake region do not run dry at intervals-through subterranean passages.
The lake region apparently represents a stage in the lowering of the land surface through solution.
In sections where the limestone occurs nearer the surface a slightly different type of lake occurs. As examples of this secon.1 type may be mentioned Alachua Lake in Alachua County; Alligator Lake in Columbia County; Lake Miccosukee in Jefferson County, and Lakes Jackson, Lafayette and Iamonia in Leon CountyN. These lakes have been described in a preceding paper in this volme.
CLIMATE.
The counties of Florida covered by this report lie bordering the Atlantic Ocean and are favorably located for a mild and equable climate. The heat of summer as elsewhere in Florida is tempered by the proximity to the ocean. By varying the crops the growing season can be made to extend practically throughout the year.
TEMPERATURE.
As the total length of the section covered by this report extends north and south fully 250 miles the temperature varies appreciably between northern and southern points. At Jacksonville in Duval County, within about 25 miles of the north line of the State, the mean annual temperature is 69 degrees Fahrenheit. The means for the four seasons of the year are as follows: Winter 56. Spring 69; Summer 81; Fall 70. The absolute maximum for summer heat recorded at Jacksonville is 104, although temperatures above ioo are rare. The lowest temperature recorded is io above zero. The mean temperatures for the several months of the year at Jacksonville are as follows: January 55 February 58; March 63: April 68; May 75; June 8o; July 82; August 82; September 78; October 71; November 62; December 56.