54 E. E. ROSAIRE AND O. C. LESTER, JR. 
bottom of the water, or buried in a hole on shore. A smaller simul- 
taneously detonated surface charge was used for the air wave dis- 
tance determination. Travel times were read to hundredths of a 
second. 
Distance determinations were made from the travel times for the 
air waves, corrections being used for wind velocities and directions, 
determined by compass and hand anemometers at the time of each 
shot. For short-shot lengths, up to about 5 miles, these were relatively 
accurate to about 200 feet. (At greater distances over land, large errors 
J pee 
\Mieecane 

Fic. 2.—Travel time data for Vermilion Bay. 
appeared in this method, as for instance, when an error of 2,000 feet 
appeared in a shot line 40,000 feet long.) 
Distance determinations and final travel-time counts were made 
at headquarters in the houseboat. The travel-time data (Fig. 2) were 
plotted, and the normal relationship indicated by drawing the obvious 
“normal” travel-time curve. Travel times appreciably shorter than 
normal were then considered as suggesting the existence of a salt 
dome, and bona fide time differences checked by a cross fan. 
INTERPRETATIVE PROCEDURE 
Long distance refractions ——The data collected in Vermilion Bay 
may be taken as typical of a shallow Gulf Coast salt dome. For con- 
venience of study, the time intervals are plotted, on each line, from 
384 
