ANNUAL REPORT—GEOLOGY. ^3 
n 
streams from the ’glades cut across it. Its present alti¬ 
tude is due to a mild elevation of the east coast which 
occurred probably during or at the close of Pleistocene 
time. 
The recent formations in the State include rock accu¬ 
mulations of several varieties. Loose sands are not infre¬ 
quently firmly cemented by the iron deposited from 
chalybeate springs. A rock so formed, although compara¬ 
tively recent, may nevertheless be extremely hard. An 
example of such rock containing numerous snails is found 
along Sarasota Bay. Marl deposits have been observed to 
accumulate at the point of meeting of fresh and salt water. 
Coquina rock forms as a result of the more or less com¬ 
plete cementation of masses of shells. Sand dunes occur 
along both the east and the west coasts, while shell 
mounds and Indian remains are found in many places. 
Fossils Contained in the Florida Formations. 
The fossil record contained in the rocks of Florida is 
above the average in completeness. This is especially true 
of the marine invertebrate fauna. From the Oligocene 
period to the present time there is an almost unbroken 
series of rock formations made up largely of the remains 
of such marine invertebrates as lived during the time of 
the formation of these rocks. W. H. Dali says :* “The 
State of Florida presents the most complete succession 
of Tertiary and post-Tertiary fossil-bearing strata of any 
part of the United States. * * * Nowhere else can 
the problems of descent with modifications during Ceno- 
zoic and later time be so well studied in the fossil and 
recent faunas.” More than fifteen hundred species of 
invertebrates have been recognized in the Florida forma¬ 
tions, and it is probable that a much larger number actu¬ 
ally occur. As early as the late Oligocene a few living 
species of marine invertebrate appear. The proportion of 
modern species in the fauna increases with each period 
from that time to the present. 
*Bnl! U. S. Geol. Survey No. 84, p. 85, 1892. 
