AGE OF THE UNDERLYING ROCKS OF FLORIDA 79 
SOURCES OF ERROR. 
In the process of drilling a well unless a casing is put in as 
drilling proceeds there is great chance of error by material falling 
down from levels above that at which drilling is actually taking 
place. Thus there is a great source of possible error, and this will 
show itself by giving too great thickness to a bed from this rea¬ 
son. On the other hand, the drill may penetrate a formation some 
distance before recognizable fossils are discovered and the range 
of the formation placed too low. A check in both of these sources 
of error is the fact that no fossils can appear in the samples until 
the, bed containing them is reached. 
In the case of Florida and the Coastal Plain in general, wells 
penetrate the same formation but once as these rocks are not 
greatly folded or faulted. Therefore, when fossils of a younger 
formation keep reappearing after an older formation is penetrated, 
it is very safe to assume that they came from the upper levels and 
do not belong with the older formations. Such specimens in the 
case of larger species are apt to become of larger size and more 
perfect when they fall from the walls above than were the spec¬ 
imens from the same, formation at the time the drill was penetrat¬ 
ing that particular bed. This is especially true of the larger num- 
mulites and orbitoids of the Oligocene and upper Eocene. 
On the whole, with the.se various sources of error constantly 
in mind it is safe to assume that very accurate and reliable knowl¬ 
edge may be obtained from the careful study of well samples. 
DATA FROM THE WELL SAMPLES. 
The location of the. fifteen areas from which well samples were 
studied from northwestern Florida to the Keys is as follows, the 
location being plotted in the accompanying map: 
1. Panama City, Washington County, 470 feet. 
2. Bonheur Development Co., near Burns Station, Waukulla County, 
2,153 feet. 
3. Jacksonville, Duval County, 980 feet. 
4. St. Augustine, St. Johns County, 1,440 feet. 
5. Anthony, Marion County, samples 50-500 feet. 
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