SECOND ANNUAL REPORT-—GENERAL, GEOLOGIC HISTORY. 
169 
difficult to determine the character of the water encountered at great 
depths because, in practically all cases, considerable fresh water enters 
the well near the surface and this would serve to dilute any salt water 
which was obtained below, and moreover, unless the head of the deep 
supplies was greater than that from shallower water bearing horizons, 
there would be a downward movement of the fresh water from the 
higher to the lower beds. However, the apparent absence of salt 
water in the deep wells of the northern part of Florida suggests that 
their included sea water has probably been drained out. The exact 
depth to which this process has extended is somewhat uncertain. 
Shaler’s estimate of nearly 1,000 feet is probably too low rather than 
too high for in a well at Sumterville hard sulphur water was en¬ 
countered at 1,386 to 1,400 feet and although the well was continued 
to a depth of nearly 2,000 feet no deeper supplies were encountered. 
At Ocala, the well of the City Water Co. which is cased to a depth of 
1,250 feet, did not encounter salt water. However, in passing from the 
central part of the peninsula toward the coast salt water is frequently 
encountered at a depth of a few hundred feet and in some wells the 
salt water comes from a depth of less than 100 feet. The salt water 
in the shallow wells may be explained by supposing that it entered the 
porous beds during the Pleistocene submergence and has not yet been 
drained away. The presence of salt water in the deeper wells near the 
coast may be interpreted in the same way, but the .explanation is much 
less certain than in the case of the shallow wells; and, possibly some of 
the saline waters of the deeper wells is sea-water included in the 
sediments when they were deposited. The deep wells all penetrate 
the limestones of Vicksburg age, and hence it is the beds of that age 
which have been drained of salt water. As a portion of these beds 
have been above sea level since Oligocene time, the salt water may 
have been removed before the Pleistocene. The magnitude of the 
emergence is not necessarily so great as 1,000 feet, because, given the 
necessary chance for escape the salt water would probably be displaced 
by fresh water, provided the surface was high enough to afford a 
small hydrostatic pressure. The absence of impervious beds of clay 
above the submarine portion of the Oligocene limestones would permit 
the escape of the water, and hence considerable thicknesses of the 
older rocks may have been filled with fresh water without being raised 
much above their present altitude. 
Since it is doubtful if the formation of large underground chan¬ 
nels extend to great depths below sea level, the large springs point to 
considerable emergence. This emergence must have been of com¬ 
paratively recent date, as, otherwise the openings would have been 
choked during the deposition of the younger Tertiary formations. 
These facts suggest that the channels of the springs were formed 
