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' lime¬ 
stone rock exposed at the surface, and having no evident subter¬ 
ranean outlet. Their origin is doubtless due to solution, 
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 subsi¬ 
dence. Any subterranean outlet that may have existed has like¬ 
wise 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 second 
type may be mentioned Alachua Lake in Alachua County; Alli¬ 
gator Lake in Columbia County; Lake Miccosukee in Jefferson 
County, and Lakes Jackson, Lafayette and Iamonia in Leon County. 
These lakes have been described in a preceding paper in this volume. 
CLIMATE. 
The counties of Florida covered by this report lie border¬ 
ing the Atlantic Ocean and are favorably located for a mild and equ¬ 
able 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 sum¬ 
mer heat recorded at Jacksonville is 104, although temperatures 
above 100 are rare. The lowest temperature recorded is 10 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 80; July 82; August 82; September 78: 
October 71; November 62; December 56. 
