ASYMMETRY OF SOUND VELOCITY 83 
correction shot on each setup from a point symmetrically placed with respect 
to two detector stations, as, for example, at a point midway between them. 
If the spacing of the stations has been properly chosen with respect to the 
local geological conditions, which can always be accomplished, the required 
correction can easily be made. 
The most difficult phase of the work is to translate the velocity readings 
into terms of degrees of dip. There seems to be no theoretical basis for a 
rigorous mathematical treatment which would accomplish this. Consequently, 
the best solution is probably an empirical calibration of the velocity values 
on some structure where the dips are accurately known. In most cases, how- 
ever, it is not of great importance to know the absolute dip. For general 
profiling and reconnaissance the direction and relative steepness of the dips 
is all that is required. The use of relative values permits comparison of the 
size of different structures, shows which side of the fold is steeper, and, of 
course, locates the crest of the fold as accurately as if precise quantitative 
dips were obtained. 
SUMMARY 
A large amount of accumulated data similar to that herein presented 
demonstrates that the method described above provides a satisfactory means 
of outlining structure in stratified and other asymmetrical deposits where 
conditions are such that the usual methods of refraction and reflection cannot 
be applied. 
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