220 The American Geologist. ^i"''- ^^"^ 
The zone thus inferred deductively is also inferred inductively 
from the disparity of cavities and rims in the case of large craters; 
but, on the other hand, there is little evidence of the wrinkling 
which, theoretically, should result from the adjustment of a cold 
crust to a cooling nucleus. * * * It is therefore probable that 
the final shrinkage of nucleus was small, and the antecedent 
storage of heat correspondingly small. During the whole period 
of growth the body of the moon was cold. 
After thus stating the hypothesis of Gilbert for the 
origin of the moon, in his own words, it is not needful to 
consider here in detail the numerous arguments which 
favor vtilcanism, instead of impacts, as the cause of the 
moon's craters. The adoption of Gilbert's explanation of 
the physiography and development of the moon would go 
very far toward conclusive verification of the planetesimal 
hypothesis ; but Chamberlin evidently thinks that volcanic 
origin of the lunar craters is more probable. 
Gilbert considers the whole - process of the moon's 
gathering its formerly scattered material to have been com- 
pleted at least before the deposition of the earth's Paleozoic 
sediments, else they would here and there reveal evidences 
of collision of some of the portions of the previous ring 
matter, since these must have fallen not only on the moon 
but in like manner on the earth. Whether the craters of 
the moon resulted from meteoric aggregation or from vul- 
canism. the very steep and high mountains of the crater 
rims have doubtless remained through very long ages un- 
aftected by agencies of erosion, because of the absence of 
atmosphere. , 
Geologic antiquity, as hitherto studied, falls far short 
of reaching back to the time of completion of the creation 
of these companion globes, the earth and its satellite, in 
nearly the same size and condition which they have now. 
But in the new views opened by the hypothesis noticed 
in this paper the range of geologic inquiries and theories 
is extended almost inconceivably farther back, through 
the laying of "the foundation of the earth." 
