136 FLORIDA GEOLOGICAL SURVEY—FOURTH ANNUAL REYORT. 
however, as the sands of the plateaus are purely residual having 
been formed in place by the decay of the underlying material, 
while the sands of the valleys are of mixed origin. In the valleys 
the sands of residual s origin have been added to by more or less 
material washed and blown from the surrounding slopes. Such 
basins are numerous and variable in size. Many are permanently 
occupied by lakes. Some of the smaller basins which have become 
so thoroughly filled with sand and other detrital material as no 
longer to contain water during any part of the year, support a scat¬ 
tered growth of live oaks and are known as “Live Oak Flats.” 
The largest of the solution basins in the county are those oc¬ 
cupied by lakes Iamonia, Jackson, Lafayette and Miccosukee, the 
latter lying adjoining the Jefferson county line. These basins, in 
season of normal rainfall, are occupied during a part of the year 
by shallow lakes, but in seasons of reduced rainfall, they become 
entirely dry, the water having escaped into the underlying limestone. 
Lake Iamonia lies near the northern line of the county. It is a 
valley or basin from one to one and one half miles wide and twelve 
or thirteen miles long, including about 6500 acres. Lake Jackson 
is irregular in outline but includes about 4500 acres. Lake La¬ 
fayette occupies a narrow valley from one-half to one mile wide 
and about five and one-lialf miles long, including about 2500 acres. 
These lakes have many interesting features in common. All occupy 
basins formed by solution. From all of them water escapes through 
sink holes into the underlying limestone. The boundaries of all 
of them are sharply marked on at least one side by abrupt bluffs, 
the basins lying from 50 to 100 feet beloAv the general level of the 
surrounding uplands. The soil in these lake bottoms is, as might 
be expected, mixed and variable in character. Those parts of the 
lakes which are frequently dry have sandy soils, the sand having 
been washed and blown in. Other parts of the basins where water 
stands during a considerable part of the year have an accumula¬ 
tion of moije or less muck, the water having acted as a preservative 
to the vegetable matter. 
The southern part of the county which differs from the northern 
part in its topographic features likewise includes different types 
of soils. In the southwestern part of the county is found an ex¬ 
tensive area, six to seven miles wide by fourteen to fifteen miles 
long, which, although sufficiently elevated, is nevertheless so level 
as to be imperfectly drained. Under these conditions a type of 
soil unlike that of the northern part of the county is developed. 
Numerous bay galls dot the surface, these being small densely 
wooded swamps. The timber growth is long leaf pine, the under- 
