138 FLORIDA GEOLOGICAL SURVEY-NINTH ANNUAL REPORT. 
connection with the ground water table. Hence fluctuation in water 
level in the lakes represents at least in a measure actual fluctuation 
in the water table, although temporary obstruction in sinks may for 
a time disconnect the basin from the ground water and for a time 
the lake level may be independent of the ground water level. How¬ 
ever, connection between the lake and the ground water in these 
large basins is the normal condition under which the basin has been 
developed. 
That there is a relation between the ground water table and the 
plane of the basin is further supported by the actual level at which 
each basin has been formed. In passing inland from the coast the 
water table rises gradually, as may be shown by well records. Lake 
Lafayette, which is about 25 miles from the coast and is the nearest 
of the present large basins to the coast, has formed a plane at 
approximately 40 feet above sea level. Lake Jackson, which is 
somewhat farther inland, has formed a basin at an elevation of 
about 75 feet above sea level. The plane of Miccosukee basin is 
probably between 75 and 85 feet above sea level, while that of Lake 
Iamonia, which is the farthest north of the large basins, lies about 
90 feet above sea level. It is thus seen that the nearer the-basin lies 
to the Gulf Coast in this area the lower the level at which the plane 
or floor of the basin is formed, and that the basin lies close to the 
water table level, probably ordinarily somewhat above that level. 
With regard to the water table the basins are at or near base level. 
In considering the history of these basins through geologic time 
it is well to bear in mind that the water table itself is subject to pro¬ 
gressive change. As the stream channels are lowered the ground 
water outlet is likewise lowered and the course of flow of the water 
to the ocean becomes more direct, and hence, the water table is low¬ 
ered owing to reduced friction of flow of the water. 
The whole, time interval available during which the physio¬ 
graphic changes in this area have taken place is probably that from 
the close of the Lower Miocene to the present. Over the northern 
part of Leon and Jefferson counties where the largest of these 
basins are found there seems to be no good evidence of the presence 
of formations later than the Alum Bluff formation, which as shown 
by its vertebrate fossils is of Lower Miocene age.* 
*Fossil Vertebrates from Florida: A new Miocene fauna; new Pliocene 
species; the Pleistocene fauna, by E. H. Sellards. Florida Geol. Survey, 8th 
Ann. Rpt. p. 91, 1916. 
