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GEOLOGY: COMMITTEE REPORT Proc. N. A. S. 
the place of observation on the earth's surface. The propagation of this 
wave-Hke movement is a matter for physical and mathematical discussion 
but the shock must also be studied in regard to its origin, the geological 
conditions under which it arises, the character of the material through 
which it is transmitted, and the conditions under which divers cata- 
strophic phenomena may be exhibited at the surface. 
Nearly all earthquake shocks are known to be due to relief or strain 
in the rocks of the earth at various depths below the surface. Such 
relief sometimes occurs in fault zones in the rocks where the geologist 
has recognized that movements have also taken place in past epochs. 
Other earthquakes are associated with volcanic disturbances. The 
source of many earth tremors cannot at present be determined. 
Volcanology deals most directly with the physical and chemical phe- 
nomena of activity at the vent. However, a volcano represents but one 
local, though important, phase of eruptive activity. Its lavas are often 
but a small part of the igneous matter involved in the movement, other 
portions consolidating beneath the surface or pouring out from fissures 
as lava floods which may not be demonstrably connected with a typical 
volcanic centre. Volcanoes are of many types of activity dependent 
upon the chemical character of the magma involved, including the asso- 
ciated gases, and on differing physical conditions. A volcano is a natural 
laboratory where the geologists, physicists, chemists, mineralogists, 
petrographers, seismologists, and other specialists have a most important 
opportunity to study a great many processes in operation which have 
been active during the entire history of the earth from the time of its 
oldest known rocks. The geologist is vitally interested in volcanic 
phenomena as he is in all current processes whose effects are visible, 
though perhaps not clearly comprehensible, in the older rocks. The 
study of extinct and more or less deeply dissected volcanoes of past ages 
and the theoretical discussions of igneous earth history point to various 
phases of volcanic activity as of particular importance. This informa- 
tion has an important bearing on the plan of investigation to be carried 
out at a volcano observatory. 
The consideration of physical processes in special relation to the de- 
velopment of the earth is now commonly called geophysics. By analogy 
we may also recognize geochemistry. Volcanology is sometimes referred 
to as a branch of geophysics but it clearly bears an equally intimate 
relation to geochemistry. The prolonged physical and chemical pro- 
cesses of volcanism result, on the material side, in volcanic rocks, minerals, 
and the volcano itself. No scheme of volcanological research is com- 
plete which does not provide for supplementing the field observations 
by studies in physical, chemical, and petrological laboratories. 
This brief and imperfect summary of the scope and relations of seis- 
mology and volcanology is designed to show that the "scientific problems 
