178 The American Geologist. ^^^rch, looi. 
hence that they finally reach and surpass the Arctic minima. In 
other words with precipitation increased equally over the whole 
planet the size of the perpetual ice-cap over the southern pole 
would finally surpass that about the northern one. "Whereas, 
then, with moderate precipitation the hemisphere with the ex- 
tremes of summer and winter climate would have the less per- 
petual ice of the two ; with more precipitation the result would 
be reversed. * * * Thus a glacial period might be pro- 
duced with us under the very same conditions which would bar 
it on Mars. It would come about in consequence of the ec- 
centricity of the orbit, but not chiefly because of that eccentrici- 
ty. Rather we may say, because of the amount of moisture 
capable of being manufactured. For were the moisture to fall 
below a definite amount, not only would no glacial period re- 
sult, no matter what the eccentricity, but actually a sort of 
anti-glacial epoch would be brought about by that very same 
cause." 
"Our survey of the Martian polar caps, then, leads us to 
some curious conclusions. It starts with apparent contradic- 
tion of Croll's theory to end in final confirmation of it. It 
comes to curse and stops to bless. But it does more. It 
shows that eccentricity of orbit by itself not only causes no un- 
iversal glaciation, but actually produces, on occasion, the op- 
posite result in more than offsetting by summer proximity what 
winter distance brings about. Eccentricity needs water, and 
a great store of it as handmaid before its glacial work can be 
accomplished. Could our earth but get rid of its oceans, we, 
too, might have temperate regions stretching to the poles." 
The vast blue-green areas of Mars are interpreted as grassy 
plains or forests. They prevail in the southern hemisphere. 
They wax and wane with the season, slightly changing their 
color. The dark bands that cross them are perhaps channels 
filled with slow running water derived from the annual dis- 
solution of the southern snow caps, wasting away toward the 
tropics. 
The eccentricity of the southern snow cap, which is marked 
from maximum to minimum, is supposed to be due to a de- 
pressed area, rather than to elevated lands. In this depression 
the permanent ice accumulates in greatest quantity, and sur- 
vives through the intense summer. N. h. w. 
