18 E. E. ROSAIRE 
of the cone of error, a satisfactory percentage of hits will be registered. 
However, when the base of the cone of error becomes greater than the 
target, the percentage of hits can be expected to fall off quite rapidly. 
At such an extended range the percentage of hits can best be raised 
by the substitution of another rifle with a smaller cone of error at the 
range now in question, rather than by trusting wholly to chance and 
continuing the use of the original rifle. 
The primary function of geophysics was the evaluation of existing 
sub-marginal prospects. The discovery of prospects by these newer 
tactics was a later function. In the usual course of events, discovery 
at a premium, i.e., at a minimum cost, is naturally expected to follow 
from the use of geophysical methods to evaluate existing sub-mar- 
ginal prospects, rather than in their use to discover as well as to evalu- 
ate prospects. 
Such was the case for each exploration campaign, except one,‘ 
in which geophysical methods made spectacular records. The first 
discovery for the torsion balance was at the Nash salt dome in Fort 
Bend County, Texas, a sub-marginal surface prospect. The first 
discoveries of shallow salt domes in the Gulf Coast Province for the 
refraction seismograph followed in rapid succession as the sub- 
marginal surface prospects at Orchard, Fannett, Hawkinsville and 
Starks were examined. In East Texas, most of the refraction discov- 
eries followed the examination of surface prospects, while the early 
successes of the reflection method on the Seminole Plateau were 
almost exclusively due to the examination of sub-marginal prospects. 
And in every case to date, with one exception,® the discoveries follow- 
ing the use of the reflection method in the Gulf Coast have been due 
to the examination of sub-marginal prospects indicated by one or 
more of the exploration methods in previous use, i.e., surface indica- 
tions, the refraction seismograph and the torsion balance. Finally, the 
4 This one geophysical exploration campaign attended by discovery at a premium, 
and unassisted by previous methods, was the refraction seismograph exploration made 
by the Geophysical Research Corporation for the account of the Louisiana Land and 
Exploration Company in the lakes and bays of Southern Louisiana. This spectacular 
success followed the extensive initial use of a method with high resolving power in virgin 
territory, wherein the number of prospects existing was undoubtedly abnormally high. 
However, after the discovery of the Lake Barre salt dome, in this same campaign, gas 
seeps were found to have been known there for many years before. 
5 And in the case of this one (unassisted) discovery by the reflection seismograph, 
at the Valentine salt dome in LaFourche Parish, Louisiana, favorable surface indica- 
tions were later found to have been known for several years over the dome itself. 
262 
