58 
FLORIDA GEOLOGICAL SURVEY-I4TH ANNUAL REPORT 
gas, the observer must use judgment as to whether or not it is probably 
coming from decaying muck at the surface or from much deeper forma¬ 
tions. Inflammable gas coming continuously with a strong flowing 
spring naturally is much more likely to be coming from a considerable 
depth than is gas that comes occasionally from swamp-mud deposits. 
GEOLOGIC INVESTIGATIONS 
The object of geologic investigation should be to determine whatever 
may be made known in regard to the property in advance of drilling or 
in addition to drilling, as the case may be. In these investigations the 
geologist will take into consideration the character of underlying sedi¬ 
ments, whether petroliferous or not, and .the probable depth of the pro¬ 
ducing horizons, if such are believed to exist. In determining probable 
structural conditions, evidence as to the position of the strata may be ob¬ 
tained by observations on the surface formations determining the direc¬ 
tion and amount of dip. Or, data may be secured from deep well rec- 
• ords in case wells have been drilled. Rarely, surface topography can be 
used to some extent to assist in determining underground structure. 
However, surface topography must be used with care. A topographi¬ 
cally high area may or may not be a structurally high area. Occa¬ 
sionally a hill or mound at the surface coincides with an anticline or 
dome in the underlying formations, but it is very unsafe to assume such 
coincidence without proof. On the other hand, many instances can be 
cited where the anticline lies in a valley, or the structural dome is a 
basin at the surface. 
In examining a property the geologist will take into account all struc¬ 
tural features that can be determined. If favorable structure of any 
kind can be demonstrated or appears probable, recommendation to drill 
will then depend upon the probable character of the underlying forma¬ 
tions. If the formations are believed to be not at all petroliferous, favor¬ 
able structure is of no significance with respect to petroleum production. 
If, on the other hand, it can be shown that petroliferous formations un¬ 
derlie the area, the location on favorable structure would be desirable. 
The character of the underlying rock may be determined from cuttings, 
from wells previously drilled, if there are such, or may be inferred from 
outcropping of formations which, although coming to the surface some 
distance away, are nevertheless known by their position and direction of 
