142 
FLORIDA STATE GEOLOGICAL SURVEY. 
Since there are no organic remains which might serve to correlate 
these beds with others, it is necessary to resort to some different means 
to determine their age. If it were possible to trace physical continuity 
between them and their fossiliferous marine equivalents, their age could 
be determined by means of the organic remains found in the latter; but 
thus far this method has been unsuccessful. However, there still re¬ 
mains a possibility of correlation by stratigraphic and physiographic 
methods. In discussing the geologic and physiographic history of the 
State, an attempt will be made to show that the Lafayette formation 
was deposited under conditions which prevailed during the deposition 
of neighboring marine and non-marine Pliocene, and that the subse¬ 
quent history of these two series of deposits has been essentially the 
same. The conclusion from this line of evidence is that the Lafayette 
is probably of Pliocene age, though it is possible that there has been 
included with it beds of similar lithological character which are older 
than the Pliocene. 
Lithologic Characters:—The materials composing the Lafayette for¬ 
mation vary from clay and fine sand to coarse sand containing small 
pebbles, the whole being commonly stained with enough oxide of iron 
to give the deposit a deep orange color. These sands and clays are 
the insoluble residue of mature weathering, which probably took place 
under physiographic conditions which favored the accumulation of the 
material in situ. Such conditions would be furnished by a surface of 
slight relief and low altitude. A subsequent increase in altitude would 
rejuvenate the streams and permit them to remove these residual pro¬ 
ducts and redeposit them in their present situation. The variation in 
physical character, together with the lenticular character of many of 
the beds and numerous instances of cross bedding show the changing 
conditions under which the Lafayette was deposited. The physical 
character of the sediments, together with the absence of marine shells 
and the sporadic occurrence of fresh water fossils suggests that the 
beds were either fluviatile or estuarine rather than marine, though the 
fact that in Florida they rise to a nearly uniform altitude may be re¬ 
garded by some geologists as an argument in favor of a marine origin. 
However, the question of the origin of the Lafayette formation is one 
of the disputed points in North American geology. Those who are fa¬ 
miliar with the non-marine deposits of the Great Plains and other simi¬ 
lar regions are inclined, for the most part, to regard the Lafayette as 
non-marine; while those who have investigated the terraces of the 
Atlantic Coast are usually ardent advocates of the hypothesis of marine 
origin. 
The solution of this problem calls for both stratigraphic and physio¬ 
graphic study of a much larger field than any single State and the re¬ 
sults obtained from the recent studies in Florida do not shed new light 
