Whether the transformation of
snow into ice be the result of pressure only, or, as I believe, quite as
much the result of successive thawings and freezings, these structural
features can equally be produced, and exhibit these relations to one
another. It may be, moreover, that, when the glacier is at a temperature
below 32 deg., its motion produces extensive fissuration throughout the
mass.
Now that water pervades this net-work of fissures in the glacier to a
depth not yet ascertained, my experiments upon the glacier of the Aar
have abundantly proved; and that the fissures themselves exist at a
depth of two hundred and fifty feet I also know, from actual
observation. All this can, of course, take place, even if the internal
temperature of the glacier never should fall below 32 deg. Fahrenheit; and
it has actually been assumed that the temperature within the glacier
does not fall below this point, and that, therefore, no phenomena,
dependent upon a greater degree of cold, can take place beyond a very
superficial depth, to which the cold outside may be supposed to
penetrate. I have, however, observed facts which seem to me
irreconcilable with this assumption.
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