THE FORMATION OF GLACIERS. 
221 
or less compact ice, the mass of which will be 
composed of an infinite number of aggregated 
snow-particles, very unequal in regularity of out- 
line, and cemented by ice of another kind, derived 
from the freezing of the infiltrated moisture, the 
whole being interspersed with air. Let the tem- 
perature rise, and such a mass, rigid before, will 
resolve itself again into disconnected ice-particles, 
like grains more or less rounded. The process 
tnay be repeated till the whole mass is trans- 
formed into very compact, almost uniformly 
transparent and blue ice, broken only by the 
intervening air-bubbles. Such a mass of ice, 
(vhen exposed to a temperature sufficiently high 
(O dissolve it, does not melt from the surface and 
fisappear by a gradual diminution of its bulk, 
» Ike pond-ice, but crumbles into its original gran- 
ular fragments, each one of which melts sepa- 
rately. This accounts for the sudden disappear- 
ance of icebergs, which, instead of slowly dissolv- 
ing into the ocean, are often seen to fall to pieces 
and vanish at once. 
Ice of this kind may be seen forming every 
winter on our sidewalks, on the edge of the little 
ditches which drain them, or on the summits of 
broad gate-posts when capped with snow. Of such 
ice glaciers are composed ; but, in the glaciei , 
another element comes in which we have not 
considered as yet,— that of immense pressure 
