OCKLOCKNEE AND AUCILLA RIVERS. 
121 
covering of muck or peat occurs over the greater part of the bottom 
of the lake. This deposit of muck reaches a considerable thickness 
in such natural depressions as occur over the lake bottom. Beneath 
the muck is usually found a deposit of light colored sand and be¬ 
neath this is the red sandy clay. 
Iamonia basin represents apparently a stream valley lowered by 
solution and enlarged laterally by subsidence through the formation 
of sinks. Originally a small stream tributary to the Ocklocknee 
River flowed through this section. In this part of the. country sol¬ 
uble limestones occur at no great distance from the surface, and in 
the course of the natural processes of erosion the stream approached 
sufficiently ne.ar this limestone to permit of the formation of sinks 
and the escape of the water of the stream through the sinks. The 
enlargement of the valley to its present size has proceeded through 
the formation and partial filling of successive sinks. As each sink 
forms, it carries down to or below the lake level, a certain small area 
of land. Moreover, the water passing through the bottom of the 
sink carries with it more or less detrital material so that the sur¬ 
rounding area is somewhat lowered by wash through the sink. In 
the course of time other sinks form, while the older sinks become 
clogged and usually partly fill up. The direction of active enlarge¬ 
ment of each lake can be. determined from the location of the recent 
sinks. As previously remarked, this rapid enlargement is usually 
around the sink which is at present actively receiving the drainage. 
The basin of this lake is 85 or 90 feet above sea level. 
JACKSON BASIN 
Jackson Basin 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 are.a of about 4,500 acres. 
The boundaries of the basin are sharply marked by the surrounding 
highlands, which rise 75 to 100 feet above the level of the lake. 
Several sinks are found in the southern half of the lake. The 
largest of these, known locally as the “lime sink,” is well out in the 
basin and in the angle between the north and east arms. An open¬ 
ing in the bottom of this sink 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 southeast from the lime sink. 
