56 FLORIDA GEOLOGICAL SURVEY-THIRD ANNUAL REPORT.
LAKE JACKSON.
Lake Jackson lies near the western border of Leon County within one and a half or two miles of the Ocklocknee River. This lake is irregular in shape, and has a total area of about 4,5oo acres. The bound. aries of the basin are sharply marked by the surrounding highlands d Ink which rise 75 to ioo feet
lake Jacsoz above the level of the
lake. Several sinks occur in the southern half of the lake. The largest of these, known locally as the "lime sink," is located Well out il the basin and in the angle between the north and east arms. (See map). An opening in the bottom of this sink Fig. 2.-Lake Jackson. in May, 1907, permitted
the water to run out, leaving the sink dry, and also draining the lake or such part of it as was connected with the sinks. An indefinitely defined broad depression or slough extends to the south-east from the lime sink. Several water holes representing old sinks occur along the line of this depression. A new sink occurred along the bottom of the depression about one mile southeast of the lime sink in June, 1907. A compact limestone showed in the bottom of this sink at a depth of about 25 feet from the surface. At the time this sink formed the lake was low, a part of the water having been carried off through (the opening which had formed in the lime sink a month earlier. All the water that could reach the new sink was carried off in the course of two or three days, leaving the lake dry except for occasional water holes. When examined in September, 1909, a small open sink was found in the slough which carried away all of the water that reached it froni the surrounding parts of the lake.