222 
THE FORMATION OF GLACIERS. 
in consequence of the vast accumulations of snow 
within circumscribed spaces. We see the same 
effects produced on a small scale, when snow is 
transformed into a snowball between the hands. 
Every boy who balls a mass of snow in his hands 
illustrates one side of glacial phenomena. Loose 
snow, light and porous, and pure white from the 
amount of air contained in it, is in this way pres- 
ently converted into hard, compact, almost trans- 
parent ice. This change will take place sooner, 
if the snow be damp at first, — but if dry, the 
action of the hand will presently produce moist- 
ure enough to complete the process. In this case, 
mere pressure produces the same effect which, in 
the cases we have been considering above, was 
brought about by alternate thawing and freezing, 
— only, that in the latter the ice is distinctly 
granular, instead of being uniform throughout, 
as when formed under pressure. In the glaciers 
w T e have the two processes combined. But the 
investigators of glacial phenomena have consid- 
ered too exclusively one or the other : some of 
them attributing glacial motion wholly to the 
dilatation produced by the freezing of infiltrated 
moisture in the mass of snow ; others accounting 
for it entirely by weight and pressure. There is 
yet a third class, who, disregarding the real prop- 
erties cf ice, would have us believe, that, because 
tar, for instance, is viscid when it moves, there- 
