94 
ICE-PERIOD IN AMERICA. 
subsequent freezing, constantly renewed, — 
and also to the sinking of the mass upon itself 
in consequence of its own weight, the lower 
portions being thus forced out by the pressure 
of the superincumbent ice. Upon an inclined 
plane the movement consequent upon these 
changes will of course be downward; but 
what would be the result, if a field of snow 
many thousand feet thick, corresponding, ex¬ 
cept in its greater bulk, to the accumulations 
by which the present glaciers are caused, were 
stretched over an extensive level surface ? 
The moisture from the upper superficial layers 
would permeate the larger mass as it now does 
the smaller one, trickling down into its lower 
portions, while the pressure from above would 
render the bottom hard and compact, chang¬ 
ing it gradually into ice. If this should take 
place under climatic conditions which would 
keep the whole as a mass in a frozen state, 
the pressure from above would force out the 
lower ice in every direction beyond its original 
circumscription, thus enlarging the area cov¬ 
ered by it, while the whole would subside in 
its bulk. Let us for a moment assume that 
such an accumulation of snow takes place 
