172 
FLORIDA STATE GEOLOGICAL SURVEY. 
nels cut in the limestone may be traced for some distance. As these channels, too 
small to make any marked feature on the usual hydrographic chart, could not 
have been cut since the sea has covered the plateau, the inference is obvious that 
they were cut before the tilting of the peninsula, when the limestone .was above 
the level of the sea. 
The drowning of the St. Johns River valley which permitted 
brackish water to extend far inland, beyond Jacksonville, shows that 
the east coast as well as the west has recently been depressed. The 
amount in either case was probably comparatively slight though it is 
difficult to obtain precise data. However, since the channel of the 
St. Johns River has a depth of at least'sixty-five feet below mean tide 
opposite Jacksonville it is safe to assume a depression amounting to 
over fifty feet. An equal amount of submergence is suggested by the 
depth of water covering the submarine spring near St. Augustine, 
and a far greater depression is suggested bv the depth of this spring 
which, as already noted, is reported to be 200 feet; but this greater 
submergence probably took place before the deposition of the Pleisto¬ 
cene sands and marls. 
Earth movements are doubtless taking place along the coast of 
Florida at the present time, but the rate of change is so slow that it 
is only under the most favorable conditions that the effects of the 
movements are noted. One of the earliest recorded observations on 
coastal changes was made by Dr. Gorrie 1 in 1884. According to this 
writer the coast at Apalachicola was gradually sinking during the 
twenty years preceding 1854. The evidence upon which the conclu¬ 
sions were based was the increased depth of water of the bar at the 
South Pass to Apalachicola Bay, and the submergence of tree trunks 
and roots, and permanent submergence of oyster reefs that were for¬ 
merly exposed at every low tide. The increase in depth of water over 
the bar at the entrance of the harbor might be accounted for by the 
action of waves and currents. If the water of the bay was prevented 
from escaping readily it is possible that the water level might have 
been raised slightly, but the deepening of „ the pass across the bar 
should have furnished a free passage for the water, and hence the sub¬ 
mergence of trees and oyster reefs was probably due to an actual 
change in the level of either land or water. The amount of submerg¬ 
ence was estimated at eight or nine inches in twenty years,, or approxi¬ 
mately seven feet per century. 
In 1902, Vaughan 2 obtained information which indicates that the 
coast in the vicinity of St. Marks has been rising within the last half 
1 Gorrie, Dr. On changes of level of the western Coast of Florida, Boston 
So©. : Nat. Hist. Proc., vol. 4, 1854, pp. 391-392. 
2 Vaughan, T. Wayland. Evidence of recent elevation of Gulf Coast along; 
the western extension of Florida, Science, n. s., vol. 16, No. 404, 1902, p. 514. 
