ASYMMETRY OF SOUND VELOCITY, 81 
little admixture of sand and has no recognizable bedding. In the locality 
where the above data originated, however, there were good reasons to suppose 
that the regional dip was eastward, in a direction away from the hills. Drilling 
subsequently indicated that such was the case for the underlying formations, 
but the seismograph results appeared to be the only definite evidence that the 
same dip existed in the mottled clay cover. Shots at 1000 meters distance 
confirmed the figures obtained from the 500 meter shots, as the following 
tabulation will show. 
TABLE V. Material: “Mottled clay”, Venezuela. Shooting distance: 1000 meters. Station spacing: 

500 meters. 
E Shots W Shots 
Apparent velocities Apparent velocities 
2320 2360 
2660 2550 
2780 2550 
2690 2580 
2940 2580 
2800 2580 
2230 
2170 
2320 
Average 2698 2436 

TESTS FOR KNOWN STRUCTURES 
Perhaps the best confirmation of any geophysical theory is its test on 
known structures. We have carried out several tests of this sort with very 
gratifying results. One of the earliest, and at the same time, one of the most 
comprehensive trials of the dip method of shooting was made on a group of 


ee tee fee 
2000 - 
é 402 104 106 106 {10 112 114 116 
fe SE Stations NW 
3 Surface c SS 
$ 5000 IIIN CS 
5 Cross-section of structure 
[-} 
& 4000 
<x 






NW Shots 
3 
3 

20 

102 104 106 108 110 112 114 116 
SE Stations NW 
Fig. 6. Dip-velocity curves across structure miocene shale—Venezuela. 
shale structures, arranged in echelon, near Maracaibo, Venezuela. These 
folds, outcropping through the mottled clay cover, had been worked out by 
surface geology, and their axes fairly well located. The seismograph was 
225 
