VELOCITY OF ELASTIC WAVES IN GRANITE 61 
in some cases as much as thirty feet beneath the surface of the water, and 
one hundred feet beneath the surface of the ground. This arrangement had 
the important advantages that the explosions were confined by the water and 
that the energy entered sound, unweathered granite. The efficient confine- 
ment of the explosions by the water made it possible to use relatively small 
TIME-DISTANCE CURVES 
QUINCY GRANITE 
n 
fo) 
z 
° 
(Ss) 
Ww 
n 
z 
Ww 
= 
= 
o. 

61-57-4\2@ 61-57-4 
58-11- 
/ © 74-67-4 
DISTANCE IN FEET 
00 

Fig. 3. 
charges. About five hundred pounds of dynamite sufficed for the entire in- 
vestigation. 
At Westerly, shooting positions were chosen where the granite was 
covered with several feet of glacial drift. There the charges were placed in 
holes dug down to the granite. 
205 
