588 GEOPHYSICS: H. S. WASHINGTON Proc. N. A. S. 
lava structures, since "aa" and "pahoehoe," the two terms most com- 
monly used, by no means cover all the types that are met with. 
VOLCANOLOGY AND GEODESY 
The apparently intimate correlation between the average chemical 
composition of the igneous rocks of the continents, oceanic floors, and of 
smaller petrographical provinces (as a means of arriving at comparable 
densities of their masses), and their elevations, together with the bearing 
of this study on the theory of isostasy, has been pointed out recently by 
the writer. W. Bowie suggests the continuation of such investigations 
"as a contribution to the study of isostasy." He also suggests the ad- 
visability of establishing gravity stations in the immediate vicinity of 
volcanoes, the selection of appropriate localities to be made with the 
cooperation of volcanologists. He thinks that there is reason to believe 
that "areas where volcanoes are active are probably in a high state of 
isostatic equilibrium," and the determination of this and analogous 
points would be of great service to both sciences. 
VOLCANOLOGY AND SEISMOLOGY 
At the outset it must be emphasized that, contrary to a wide spread 
belief, there is little connection between volcanoes and most earth- 
quakes, though their frequently contiguous localization may be due to 
one and the same cause, such as a fracturing of the earth's crust. By 
far the great majority of recorded earthquakes (it has been estimated 
at about 95%), and these the most important, are due to crustal move- 
ments and, so far as we know, have no direct connection with volcanoes 
or their activity. The small remainder of earthquakes of volcanic origin 
are mostly very local and of comparatively small magnitude. Notwith- 
standing this, the two sciences are in contact at several points. 
The study of the small number of truly volcanic earthquakes is, of course, 
intimately connected with the study of the volcanoes that produce them; 
while, conversely, the question of the influence of earthquakes as possi- 
bly initiating volcanic eruptions or other activity is an interesting field 
for study. 
The study of volcanic tremors of small amplitude and energy, during 
periods both of quiet and of eruption, is of great importance, and would 
naturally form part of the systematic, continuous study carried on at a 
volcano station, as has been done both at Kilauea and Vesuvius. This 
may be expected to be of very material aid in the future prediction of 
eruptions. For such observations some of the forms of seismographs 
and other seismological instruments, duly modified to suit the different 
conditions, are necessary, and seismological principles or data would also 
enter into the study. 
VOLCANOLOGY AND METEOROLOGY 
As has been already noted, the systematic observation of certain meteoro- 
logical data, especially barometric pressures and rainfall, would form an 
