1916] FORSAITH—ALLOCTHONOUS PEAT 33 
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to such an extent that it is not able to support the superincumbent 
sand or clay, which, falling, leaves a bowl-shaped valley. Depres- 
sions thus formed may contain more or less permanent ponds, 
known as “lime sinks,” which are often important as sources of 
peat. Examples of this type of lake production will be mentioned 
in the later discussion. 
Reference to any good map of the United States will show that 
there are more lakes in Florida than in the remainder of the coastal 
- plain, the larger number of which, curiously enough, occur in the 
higher or central regions of the state. These lakes vary in many 
respects, but may conveniently be divided into 5 classes, as follows: 
large deep and large shallow lakes of irregular outline; small 
deep and small shallow lakes of more or less circular outline, and 
filled lakes which may present an outline characteristic of either 
of the two previously mentioned types. There is a great variation 
“jn size, from Okechobee, which is the largest lake wholly in the 
United States except Lake Michigan, and Lake Apopka, with its 
62 miles of coast line, to those which are only a few rods in diameter. 
The semitropical climate of Florida is very favorable for the 
growth of peat-forming plants. There is an average temperature 
of 72° C., with a more or less uniform variation from January with 
a mean of 58° C. to that of 83° C.in July. The average rainfall is 
about 49.6 inches per annum, the greater part of which is pre- 
cipitated during the warmer months. This condition compensates 
for the loss by evaporation during the summer season, and pre- 
serves a more constant level for the lakes than would be possible 
if the greater precipitation occurred within the cooler season of 
the year. The texture of the soil, also, is very favorable for the 
formation and stability of lakes, since the porous coastal plain 
sand at once absorbs the greater portion of the rainfall, which 
gradually seeks the lower levels to reappear as permanent bodies 
of water. 2 
The object of the present investigations is to determine the 
relative amounts of allocthonous peat (that type of peat which 
has been deposited by a gradual accumulation of floated, drifted, 
and wind-blown vegetable material in permanent and more or less 
quiet bodies of open water), and of autochthonous peat (that type 
