These
observations of mine have the advantage over those of other observers,
that, while they embrace the whole extent of the glacier, transversely
as well as in its length, they cover a period of several successive
years, instead of being limited to summer campaigns and a few winter
observations. The consequence of this mode of progressing will be that
the straight lines drawn transversely across the surface of the glacier
above will be gradually changed to curved ones below. After a few years,
such a line will appear on the surface of the glacier like a crescent,
with the bow turned downward, within which, above, are other crescents,
less and less sharply arched up to the last year's line, which may be
again straight across the snow-field. (See the subjoined figure, which
represents a part of the glacier of the Lauter-Aar.)
[Illustration]
Thus the glacier records upon its surface its annual growth and
progress, and registers also the inequality in the rate of advance
between the axis and the sides.
But these are only surface-phenomena. Let us see what will be the effect
upon the internal structure. We must not forget, in considering the
changes taking place within glaciers, the shape of the valleys which
contain them.
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