If the snow be loose and porous throughout, the
water will pass through its whole thickness, accumulating at the bottom,
so that the lower portion of the mass will be damper, more completely
soaked with water, than the upper part; if, on the contrary, in
consequence of the process previously described, alternate melting and
freezing combined with pressure, the mass has assumed the character of
icy snow, it does not admit moisture so readily, and still farther down,
where the snow is actually transformed into pure compact ice, the amount
of surface-water admitted into its structure will, of course, be greatly
diminished. There may, however, be conditions under which even the
looser snow is comparatively impervious to water; as, for instance, when
rain falls upon a snow-field which has been long under a low
temperature, and an ice-crust is formed upon its surface, preventing the
water from penetrating below. Admitting, as I believe we must, that the
water thus introduced into the snow and ice is one of the most powerful
agents to which its motion is due, we must suppose that it has a twofold
influence, since its action when fluid and when frozen would be
different.
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