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GEOPHYSICS: R. B. SOSMAN 
Proc. N. a. S. 
edge of the character and chemical composition of the rocks of the moon, 
and thus possibly a decision of the question of the volcanic or non-volcanic 
origin of its "craters," might conceivably be arrived at by astronomers, 
through study of the maximum polarization angle of various portions of 
the moon's surface, such as the floors of the "seas" and the "walled 
plains." From the determination of this, calculation of the index of 
refraction of the material is a simple matter. The difference between 
the refractive index of a rhyolitic glass (ca. 1.490) and that of a basaltic 
glass {ca. 1 . 590) is so great that it would seem to be possible to obtain 
some general or at least roughly approximate knowledge of the general 
composition of the surface rocks of the moon, especially if they are 
glassy lavas. We should be able, in any case, to determine thus whether 
all parts of the moon's sur face are composed of the same material. 
AN OUTLINE OF GEOPHYSICAL-CHEMICAL PROBLEMS 
The subject-matter of geophysical-chemistry may be defined as "the 
physical properties and chemical reactions of the substances and aggre- 
gates that make up the earth". It may therefore be roughly divided 
into two parts: A. Properties and reactions of materials accessible at 
the earth's surface. B. Properties and reactions of materials in the 
earth's interior. 
Each of these may again be sub-divided as follows : 
1. Properties and reactions of individual chemical substances; for 
example, the silicate minerals. 
2. Properties and reactions of aggregates; for example, oceanic water, 
silicate rocks. 
3. Properties and reactions of larger units of matter; for example, 
glaciers, batholiths. 
A relatively small number of "common" oxides serves to make up prac- 
tically 98% by weight of the outer ten miles of the lithosphere. All the 
other elements and compounds known to chemistry are included in the 
remaining 2%. From the geochemical standpoint, therefore, we may 
divide chemical substances into two classes: "abundant" and "rare." 
The "abundant" oxides are, in the order given by averages of a great 
many analyses of terrestrial rocks, as follows: 
By Robkrt B. Sosman 
A. MATERIALS AT THE EARTH'S SURFACE 
Chemical Substances 
