THE AGE OF THE UNDERLYING ROCKS OF FLORIDA 
AS SHOWN BY THE FORAMINIFERA OF WELL 
BORINGS. 
JOSEPH A. CUSHMAN. 
After the discovery of foraminifera indicating older forma¬ 
tions than had hitherto been found in Florida in well borings sent to 
me through the U. S. Geological Survey* the State Geologist, Dr. E. 
H. Sellards, asked me to undertake a study of various well borings. N 
It was hoped that a study of the foraminifera of these samples 
from different parts of the State would reveal the presence of beds 
of definite age and add to our knowledge of the geologic structure 
of the Florida peninsula. 
In all there were submitted to me well samples from fifteen 
localities widely scattered over the State. While these localities 
represent a very small amount of data compared to the areal extent 
of Florida, they are so located that taken together they give a 
skeleton on which may later be built up a detailed geologic structure. 
The data for the various wells will be given and then they will be 
followed by a general interpretation of what the foraminifera 
have to show as to the age of the various rocks penetrated. First 
however a few cautions as to the use of well samples may not be 
out of place. 
SPECIAL FIELD OF THE FORAMINIFERA. 
In the process of well drilling the larger fossils are often 
ground into fragments too small to be of any value for specific 
determinations and therefore for determining definitely the age of 
the rocks penetrated. Of other groups likely to escape breakage 
the bryozoa and foraminifera are probably the only two found in 
quantity. Although ostracoda often escape damage by the drill 
they are not usually in great enough numbers in enough various 
horizons to be equal in value to the other two. Of the two groups 
*This material from the Bushnell well was sent me by the Florida Survey 
through the U. S. Geological Survey. 
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