SECOND ANNUAL, REPORT—GENERAL GEOLOGIC HISTORY. 165 
limestones at other localities, especially in the central part of the 
peninsula, but it is, in general, much less abundant than in the lime¬ 
stones of Vicksburg group. 
The period of deposition which is represented in the beds of the 
Apalachicola group, was terminated by an emergence of the northern 
and eastern, parts of the State, but deposition may have continued on 
the southern margin of west Florida, where there is some evidence of 
a gradual transition between the Oligocene and Miocene beds. The 
amount of erosion which took place at this time can not readily be 
determined, but the faunal break is so marked that it indicates im¬ 
portant changes in the physical geography of the continent. It is not 
possible to state just how much Florida was affected by the forces 
which produced the changes then taking place in the West Indies and 
Panama, but its general altitude was probably considerably altered bv 
the earth movements which caused these changes. The elevation of 
the Isthmus at the close of the Oligocene affected Florida indirectly by 
changing the direction of ocean currents and thus producing a marked 
change in the fauna of the Miocene beds. Of the faunal changes at 
the close of the Oligocene Dali says : 1 
As indicated by the changes in the fauna, the physical changes attending 
the close of the Oligocene were at first slow, allowing a certain element of transi¬ 
tion to appear in the Oak Grove of uppermost Oligocene fauna. At the last they 
appear to have been sudden, at least the change in the fauna on the Gulf coast 
was absolute and complete.. The change was not only in the species and prevalent 
genera of the fauna, but a change from a subtropical to a cool temperature 
association of animals. Previously, since the beginning of the Eocene, on the 
Gulf Coast the assemblage of genera in the successive faunas uniformly indicates 
a warm or subtropical temperature of water, and the sediments uniformly show, 
from the Jacksonian upward, ( a yellowish tinge due to oxidation. In the Oak 
Grove sands come the first indications of a change towards the gray of the Mio¬ 
cene marls. With the incursion of the colder watdr the change becomes complete. 
Not only do northern animals compose the fauna, but the southern ones are 
driven out, some of them surviving in the Antilles to return later. Some change 
along the northern coast permitted an inshore cold current to penetrate the 
Gulf, depositing on the floor of the shallow Suwanee Strait, separating the 
island of Florida from the continental shore, a thin series of Miocene sediments, 
which were also carried as far south as Lake Worth on the east; coast of Florida 
and Tampa on the west coast, as shown by artesian borings. 
At the close of the Oligocene the State of Florida appears to have 
had the same general form that it now has though its area was 
doubtless less than it is at the present time. With the inauguration 
of the Miocene there came a submergence which appears to have 
reduced the land area to a narrow strip along the northern end of the 
1 Dali, Wm. H., Wagner Free Institute of Science, Trans,, vol. iii, pt. 6 , 1903, 
pp. 1549-1550. 
