44 
PACIFIC SCIENCE, VoL XXII, January 1968 
locities which are higher than basalts and lower 
than eclogites. Lower velocities of diabases com- 
pared with gabbros are primarily related to dif- 
ferences in chemical composition. 
ACKNOWLEDGMENTS 
I am indebted to Professor Francis Birch for 
the use of the facilities at Hoffman Laboratory, 
Harvard University. Dr. Joseph Martinez con- 
tributed the samples of basalt for the study. The 
study was financed, in part, by the Advanced 
Research Projects Agency of the Air Force 
Office of Scientific Research through contract 
SD-88. 
REFERENCES 
Birch, F. i960. The velocity of compressional 
waves in rocks to 10 kilobars, 1. J. Geophys. 
Res. 65:1083-1102. 
• 1961. The velocity of compressional 
waves in rocks to 10 kilobars, 2. Ibid. 66: 
2199-2224. 
Christensen, N. I. 1965. Compressional wave 
velocities in metamorphic rocks at pressures 
to 10 kilobars. Ibid. 70:6147-6164. 
1966^. Compressional wave velocities 
in single crystals of alkali feldspar at pres- 
sures to 10 kilobars. Ibid. 71:3113-3116. 
1966A Elasticity of ultrabasic rocks. 
Ibid. 71:5921-5931. 
Clarke, S. P. 1966. Composition of rocks. In: 
Handbook of Physical Constants, Geol. Soc. 
Am. Memoir 97, pp. 1-5. 
Coleman, R. G., D. E. Lee, L. B. Beatty, 
and W. W. Brannock. 1965. Eclogites and 
eclogites : their differences and similarities. 
Bull. Geol. Soc. Am. 76:483-508. 
Kanamori, H., and H. Mizutani. 1965. Ultra- 
sonic measurements of elastic constants of 
rocks under high pressures. Bull. Earthquake 
Res. Inst, Tokyo Univ. 43:173-194. 
Manghnani, M. H., and G. P. Woollard. 
1965. Ultrasonic velocities and related elastic 
properties of Hawaiian basaltic rocks. Pacific 
Sci. 19(3) :291— 295. 
Nockolds, S. R. 1954. Average chemical com- 
positions of some igneous rocks. Bull. Geol. 
Soc. Am. 65:1007-1032. 
