120 E. E. ROSAIRE AND JOSEPH L. ADLER 
correlation of reflection depths holds forth little promise as a method 
of procedure in areas where oil production is sought from these strata. 
As a general rule, records of the reflections in these beds from two 
near-by shot points show little or no correspondence of reflection 
events. Records from adjacent shot points are no more correlatable 
than average well logs in those areas. In areas where the lower Terti- 
ary is within reach of the drill, however, as on the so-called Conroe 
trend, it is sometimes possible to match reflections, and to contour 
depths on some persistent reflecting horizon with a considerable degree 
of confidence. 
On the other hand, the salt-dome province of the Gulf Coast is in 
general characterized by localized structures of great relief. As a rule, 
there is very little surface topography, and the surface aerated layer 
is generally thin and uniform. Finally, the average velocity down 
through the geological column is a minimum, as compared with that 
of the Mid-Continent. All of these factors favor the accurate deter- 
mination and use of the dip of the reflecting beds in mapping struc- 
ture, a method which at present seems to be the one which holds the 
greatest promise for detailing sedimentary structure above the more 
deeply buried salt domes. 
CORRELATION METHODS IN REFLECTION SURVEYS 
Several investigators prior to 1926 had experimented in the use 
of reflections, but the general use of the method at present is un- 
doubtedly closely associated with the success of the methods de- 
veloped by the Geophysical Research Corporation. 
This work was initiated in 1926 by J. E. Duncan, on the Nash 
salt dome in Fort Bend County under the supervision of J. C. Karcher. 
He continued his efforts there and in other areas in the Gulf Coast 
and in the Balcones fault zone, although his success was only promis- 
ing, to say the least. However, due both to accumulated experience 
and perhaps to the chance to work on better defined problems, his 
results improved as he moved back into the hard-rock country, until 
he was getting fair reflections from the Viola limestone at Seminole. 
During the following two years, the Geophysical Research Corpora- 
tion, in conjunction with the Amerada Petroleum Corporation, 
steadily worked on the problem, with regular improvements in tech- 
nique. To-day’s reflection technique is essentially that developed by 
the Geophysical Research Corporation during these two years, and 
on the whole, the use of dip shooting is really the only new departure 
from the interpretation methods established in Oklahoma from 1927 
to 1929. 
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