INTERPRETING RESULTS ON DEPTH CALCULATION 49 
it was possible to choose a primary wave and designate it as the 
second horizon impulse and also choose a secondary wave and con- 
cider it as a primary wave from the third horizon. If the second hori- 

PLATE 4.—Seismograms for profile D. 
zon had been omitted from the calculations, the total depth to the 
basement would have been too small and the surface horizon would 
appear much thicker. Omission of the third horizon from the calcula- 
tion would also have made the total depth to the basement too small 
but would not have changed the thickness of the surface horizon. 
379 
