' 54 FLORIDA GEOLOGICAL SURVEY—THIRD ANNUAL REPORT. 
it joins the Ocklocknee River, the lake is largely surrounded by the 
red clay hills characteristic of this part of the State. These hills 
rise to an elevation of from 50 to 75 feet above the level of the 
lake. 
Fig. 1.—Sketch map showing the location of lakes Iamonia, Jackson, 
Lafayette and Miccosukee in Leon and Jefferson Counties. 
The sink through which the water escapes from this lake occurs 
along the north border. When visited May 7, 1910, the sink was 
practically dry, having only a small amount of water in the bottom. 
Limestone rock, probably of Upper Oligocene age, is exposed near 
the bottom of the sink, the water escaping through or under these 
rocks. Above the limestone partly decayed sandy clays occur. 
These contain few fossils, although oyster shells were found in 
abundance at one locality. The total depth of the sink below the 
general level of the lake is not less than 50 feet. The sink occurs, 
as is usual in this type of lake, facing an abrupt bluff 30 feet 01- 
more in height. A considerable number of sinks occur around the 
border of the lake especially in the vicinity of the one large sink 
which receives 'the drainage of the lake. The formation of these 
sinks is doubtless due, as previously stated, to the fact that the water 
entering the drainage sink spreads laterally in the underlying lime¬ 
stone and dissolves the rock rapidly. The result is the formation by 
subsidence of numerous sinks adjacent to the drainage sink. The 
presence of these sinks also indicates the manner of enlargement of 
the lake basin, and indicates in each case the direction of most 
rapid enlargement at the present time. At other times the enlarge- 
