In the autumn, when the dust of a whole season has
been accumulated upon the surface of the preceding winter's snow, the
extent of the layer which year after year will henceforth crop out lower
down, as a dirt-band, may best be appreciated.
Beside the snow-layers and the sheets of dust alternating with them,
there is still another feature of the horizontal and parallel structure
of the mass in immediate connection with those above considered. I
allude to the layers of pure compact ice occurring at different
intervals between the snow-layers. In July, when the snow of the
preceding winter melts up to the line of perpetual snow, the masses
above, which are to withstand the summer heat and become part of the
glacier forever, or at least until they melt away at the lower end,
begin to undergo the changes through which all snow passes before it
acquires the character of glacial ice. It thaws at the surface, is
rained upon, or condenses moisture, thus becoming gradually soaked, and
after assuming the granular character of _neve_-ice, it ends in being
transformed into pure compact ice. Toward the end of August, or early
in September, when the nights are already very cold in the Alps, but
prior to the first permanent autumnal snow-falls, the surface of these
masses becomes frozen to a greater or less depth, varying, of course,
according to temperature.
Pages:
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280