400 THOMAS C. CHAMBERLIN 
outgrowth, thrust, and deformative shift, the total diastrophism 
appears even greater than that inferred from the preceding data. 
The concurrent import of all lines of evidence is that the total 
diastrophism of the earth was very great, but a more compre- 
hensive and quantitative mode of estimate is needed, and especially 
one that covers the diastrophism of the formative stages, in respect 
to which these lines are very weak. 
‘DIASTROPHISM ESTIMATED BY PLANETARY COMPARISON 
29. A comparative study of the volumes and densities of the 
earth and its neighbors affords an entirely independent mode of 
estimate and gives definite quantitative results." 
30. If the moon were built up of moon-stuff—having its present 
mean density of 3.34—to a sphere whose mass equaled that of 
the earth, it would have a volume of 430,353,000,000 cubic miles, 
while the actual earth’s volume is only 259,924,000,000 cubic miles. 
To reduce the hypothetical moon-earth to the volume and density 
of the real earth would require a shortening of the radius of 725 
miles and of the circumference of 4,555 miles.’ 
31. If Mars were built up of Mars-stuff at its present mean 
density of 3.58 to a spherical body of the mass of the earth, it 
would have a volume of 401,502,000,000 cubic miles. To compress 
this to a body of the density and volume of the earth would involve — 
a shortening of its radius of 618 miles and of its circumference of 
3,883 miles. 
32. If Venus were similarly built up of its own material to a 
mass equal to that of the earth, its volume of 289,506,000,000 
cubic miles would have to be shrunk radially 177 miles, and cir- 
cumferentially 1,r12 miles, to have the volume and density of the 
earth. . 
33. The earth, moon, Mars, and Venus revolve in a tract whose 
total width is less than 3 per cent of the radius of the planetary 
system. They were, therefore, probably formed under much the 
same dynamics, of much the same kinds of material, and in much 
«The Order of Magnitude of the Shrinkage of the Earth Deduced from Mars, 
Venus, and the Moon,” Article X, Jour. Geol., Vol. XXVIII (1920), pp. 1-17. 
2 [bid., p. 13. 
