100 
FLORIDA GEOLOGICAL SURVEY—THIRD ANNUAL REPORT. 
about the average rainfall, and 53 inches may be safely assumed as 
a close approximation to the annual rainfall for this section.* 
DISPOSITION OF RAINFALL. 
Of the total rainfall of any area (1) a part is returned as 
vapor to the atmosphere without having entered the earth; (2) a 
part is carried off by streams and rivers to the ocean without pene¬ 
trating the earth; (3) a part is absorbed into the earth. 
(i) WATER EVAPORATED WITHOUT ENTERING THE EARTH. 
Immediately following a rain the atmosphere is nearly or quite 
saturated. The evaporation at this time is slow, and the part re¬ 
turned to the atmosphere directly from the land is an almost neg¬ 
ligible amount. This is especially true of a soil into which the 
water enters quickly. Some of the water clinging to the leaves 
of plants is re-evaporated, as well as a part of that which falls 
into lakes, ponds and temporary pools. While an estimate of the 
amount evaporated must be regarded as only in the roughest way 
approximate, yet it is probably safe to assume that not more than 
two or three per cent, of the total rainfall is returned to the atmos¬ 
phere by direct evaporation without having entered the earth. 
( 2 ) SURFACE RUN-OFF. 
The relative proportion between the surface run-off and the 
surface in-take of water is dependent upon the character of the 
surface and the deeper formations and upon the topography. The 
former affects rapidity of in-take of water into the earth; the 
latter the rapidity of surface run-off. 
With regard to topography eastern Florida is either flat or 
rolling. Rarely can a locality within this section be described 
as hilly. The elevation increases gradually from sea level at the 
coast to a maximum of scarcely more than 200 feet inland, while 
large sections are so flat as to present no perceptible slope. To¬ 
pographically the conditions are, therefore, very unfavorable to 
surface run-off. 
On the other hand, the conditions are exceptionally favorable 
to large surface in-take. A mantle of sand, forming the surface 
^Deduced from the U. S. Weather Reports. Precipitation: Average, 
Greatest and Least Monthly Amounts, from the Establishment of Stations to 
the End of 1904. Wm. B. Stockman. 
