54 FLORIDA GEOLOGICAL SURVEY-THIRD ANNUAL REPORT.
it joins the Ocklocknee River, the Iake is largely surrounded by the red clay hills characteristic of this part of the State. These hills rise to an elevation of from 5o to 75 feet above the level of the lake.
Fig. I- Sketch map showing the location of lakes Jamonia, 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, 19IO, 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 or 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 limestone 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 o E the lake basin, and indicates in each case the direction of most rapid enlargement at the present time. At other times the enlarge-