170 
FLORIDA STATE GEOLOGICAL SURVEY. 
during the post-Pliocene.. It is believed that they date from the uplift 
which permitted the erosion of the deep valleys of the large streams 
of northern Florida. 
Concerning the probable changes of level in Florida Dali says i 1 
The, on the whole, remarkable horizontality of the Florida strata indicates 
a freedom from violent changes of level from the time the Peninsular limestone 
first emerged from the sea. Landshells in the Ocala limestone show that then 
dry land existed. South of the Suwannee Strait, closed in late Miocene times, 
there is no evidence of subsequent submersion to any serious extent. Two 
gentle flexures run parallel with the peninsula/having the lake district between 
them; a tilting of, at the most, thirty feet, up at the east, down at the west, 
which may have been contemporaneous with the flexures; and, for the rest, very 
slow and slight but probably nearly continuous elevation never exceeding one 
hundred feet and perhaps less than half that, with dry land and fresh-water 
lakes constantly existing since the Ocala islands were raised above the sea; such 
is the geological history of the Florida peninsula. Denudation of the organic 
limestones by solution rather than erosion is the prominent characteristic of the 
changes in the surface. Soft, crumbling under the finger-nail the rocks of the 
plateau, if lifted five or six thousand feet, as claimed by Dr. Spencer, would have 
been furrowed by canons and swept bodily into the sea. Indeed, to me the 
proposition is inconceivable as a fact and incompatible with every geologic and 
paleontologic fact of south Florida which has come to my knowledge. 
If the Lafayette beds which form the surface of considerable areas 
in north Florida were deposited when the surface had a low altitude, 
the subsequent uplift, to permit the streams to cut their valleys to their 
present depth, would amount to approximately 250 feet near the 
northern line of the State; and since the streams appear to have cut 
below the levels of their present flood plains this estimate may be 
regarded as too low by an amount which, owing to the absence of 
satisfactory data, is yet undetermined but is probably not great. 
The erosion interval which began in the early Pleistocene or late 
Pliocene, was succeeded by a slight submergence which permitted the 
sea to cover the southern end of the State northward to some distance 
beyond Kissimmee, though the ridge upon which Lakeland is situated 
probably remained out of water either in the form of an island or a 
long, narrow peninsula. The St. Johns valley was also occupied by 
the sea and the land to the east of it may have been again submerged. 
A strip -of land of varying width along the Gulf coast was also covered 
and the sea extended into the valleys of all the large streams forming 
estuaries which were more extensive than those of the present day. 
During the interval of extensive erosion the Lafayette upland had 
been considerably dissected and its materials had been deposited in 
the valleys which were being excavated. With the inauguration of 
1 Dali, Wm. H.,Tertiary Fauna of Florida: Wagner Free Institute of Science,. 
Phila., vol. 3, pt. 6, 1903, pp. 1545-1546. 
