70 L. D. LEET AND W. M. EWING 
maximum velocity in the “granitic layer” to depths where the pressure is 
greater than 2000 megabars. We are accordingly forced to conclude that 
either the “granitic layer” is not granitic, or granite does not exhibit such 
rapid changes in compressibility at pressures below 2000 megabars. It ap- 
pears that, whether or not we consider statically and dynamically determined 
compressibilities equivalent, the observed compressibility of Quincy granite 
is not comparable with the low-pressure part of the Adams and Williamson 
curve. 
The good agreement between the compressibility measured at Quincy by 
a dynamic method and that measured statically by Adams and Williamson 
suggests that the marked discrepancy between static and dynamic values 
which has been reported? does not exist for granite. It should be noted that 
though the only quantities which they measured were the compressibility 
and density, on page 520 of their paper they have computed the velocities 
of seismic waves in the rocks they studied. The values which they show for 
the velocities depend upon the value 0.27 which was assumed for Poisson’s 
ratio. If the value 0.333, which was determined at Quincy, were substituted 
in their computations, the resulting velocities would be in agreement with 
those determined in the present investigation. 
XI. ACKNOWLEDGMENTS 
The investigation was conducted by the Harvard Seismograph Station 
during the summer of 1931. The instruments used were built and patented 
by H. Gordon Taylor in the name of the Geophysical Exploration Company. 
They were purchased through generous gifts from Mr. Edward Mallinckrodt, 
Jr., chairman of the Committee to Visit the Division of Geology at Harvard, 
and Professor R. A. Daly. The cost of the balance of the field equipment and 
all operating expenses were met by a grant from the Milton Fund of Harvard 
University. 
We are indebted to the Atlas Powder Company for permission to shoot 
on their property at Quincy, to the Rockport Granite Company for permis- 
sion to use their property at Rockport, and to Mr. John H. Austin for per- 
mission to run our Westerly profile on his property. Their ready cooperation 
was an important factor in making possible the rapid and successful com- 
pletion of the program. 
BIBLIOGRAPHY 
1F, D. Adams and E. G. Coker, “An Investigation into the Elastic Constants of Rocks, 
More Especially with Reference to Cubic Compressibility”. Carnegie Institution of Washington 
Publication No. 46, 69 pages (1906). Washington, D. C. 
2L. H. Adams and E. D. Williamson, “The Compressibility of Minerals and Rocks at 
High Pressures”, Journal of the Franklin Institute, 195, 475-529 (1923). Reprinted as No. 
484 of Papers from the Geophysical Laboratory, Carnegie Institution of Washington, Press of 
J. B. Lippincott Company, (1923). 
3 B. Brockamp and Mothes, H., “Seismische Untersuchungen auf dem Pasterzegletscher” 
Zeitschrift fiir Geophysik 6, 485 (1930), Géttingen. 
“R. A. Daly, “The Effective Moduli of Elasticity in the Outer Earth-Shells”, Gerlands 
Beitrage zur Geophysik 19, 194-209 (1928). 
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