EARLY HISTORY OF GEOPHYSICS 
cher’s early ideas on the subject since one of Udden’s sons was a 
fellow in physics at the University of Pennsylvania, and a colleague 
of Karcher, who had communicated ideas on the subject to him. 
During 1925, practically all of the commercial work was being 
done by Seismos. In November of that year three crews were oper- 
ating for the Gulf and one crew for Marland. The Humble was de- 
veloping its own instruments and McCollum was in the field during 
the latter part of the year. The Seismos crews were using mechanical 
seismographs, surveying positions, and estimating time of shot ex- 
plosions by sound through the air. Karcher introduced the electrical 
seismograph, determined the time of skot explosion by radio and 
used the air sound waves for surveying position, innovations which 
became standard practice within the year. 
The real success of the refraction type of seismic surveys, and 
one of the most brilliant successes for geophysical prospecting yet 
scored by any method was the intensive campaign of searching for 
shallow salt domes which swept the Gulf Coast of Texas and Louisiana 
from 1924 to 1930. This campaign was initiated with the appearance 
in the Gulf Coast, in March, 1924, of the Mintrop crew working for 
the Marland Oil Company. This crew was soon followed by another 
Mintrop crew for the Gulf Production Corporation under the general 
direction of L. P. Garret. 
Mr. Garret had conceived the idea of using seismic refraction sur- 
veys as a tool to prospect for salt domes as early as 1905-06 and to- 
gether with Mr. Robert Welch of Houston, had made inquiries as to 
instruments and methods. Instruments were expensive and not really 
adapted to work on the scale required and so the matter was dropped. 
When the Mintrop crews appeared in the United States, however, 
they found in Mr. Garret one who was already quite convinced as 
to the possible value of the method, and one who was in position to 
use them broadly and earnestly. The Gulf Coast with its types 
of rocks-clays, shales, and sands, having a linear velocity of sound 
transmission of around 6,000 feet per second and rock salt with a 
corresponding velocity of 15,000-16,o00 feet per second, was an 
ideal region for the method. The outstanding success of the method 
and indirectly of the introduction of geophysical methods into the oil 
business, owes much to the peculiar suitability of the area where it 
was tried and to the vigorous support given by Mr. Garret. 
The seismic or sonic method was by no means new. A little less 
than a century ago, Robert Mallet, one of the fathers, if not the 
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