DEC. 19, 1923 WASHINGTON: DENSITY OF EARTH 455 
appears to have thought, judging from the conspicuous flows on the 
surface, that they represented well the bulk of the rocks of the volcano. 
In this I think that he is in error, because my examination of the deep 
ravines cut by erosion in the eastern flank of Mauna Kea showed 
“the almost.complete absence of ash and scoria beds” and the over- 
whelming prevalence of compact or but very slightly vesicular forms 
of lava among the interior flows. It is therefore probable that my 
specimens, most of which were compact or in which vesicularity was 
compensated for by pulverization, represent the mass of the volcano 
far better than do Preston’s surface specimens of pahoehoe or the 
rough aa crust, conspicuous forms that a non-geologist would naturally 
collect. 
In the next place, Preston seems to be scarcely justified in using 
Dana’s data for Mauna Loa and Kilauea in discussing the density of 
Mauna Kea. My recent study has shown that the general petro- 
graphical and chemical characters and the average densities of the 
five voleanoes on Hawaii are markedly different the one from the 
other. Thus, to confine our attention only to densities, I obtained 
the average specific gravity 2.969 for Mauna Kea, 2.932 for Kilauea, 
2.953 for Mauna Loa, and 2.940 for the whole island of Hawaii. 
The differences are not great, but they are so marked that they should 
be taken into account. 
Five years earlier than his study at Mauna Kea, Preston,!! from 
pendulum observations at Haleakala on Maui, obtained the value é = 
0.48A at this voleano, which was considered as a cone. From this, 
accepting the value of A as 5.67, he calculates the average density of 
the rocks of Haleakala as 2.72. 
This average specific gravity seems much too low, and that derived 
from the specimens that he collected, (2.21) is certainly far below the 
true value, as may be seen from the individual specific gravities and 
from Merrill’s descriptions, which indicate that most of Preston’s 
Haleakala specimens were either very vesicular or not fresh. I have 
therefore determined the densities of nine specimens of lava from 
Haleakala that were collected in 1920 by Dr. J. Allan Thomson and 
kindly. given by him to me for study.’2 The freshest, most compact, 
and the most representative specimens, so far as could be judged 
without microscopical examination, were selected. The determina- 
4K. D. Preston in U. S. Coast and Geodetic Survey, Report for 1888, Appendix No. 
14, p. 5380. 1889. He gives a slightly lower value (0.43) in Amer. Journ. Sci. 36: 311. 
1888. 
#2 These will be described, with analyses, in a forthcoming paper in my series on the 
petrology of the Hawaiian Islands. 
