A glacier lies in a deep trough, and the tendency of the
mass will be to sink toward its deeper part, and to fold inward and
downward, if subjected to a strong lateral pressure,--that is, to dip
toward the centre and slope upward along the sides, following the scoop
of the trough. If, now, we examine the face of a transverse cut in the
glacier, we find it traversed by a number of lines, vertical in some
places, more or less oblique in others, and frequently these lines are
joined together at the lower ends, forming loops, some of which are
close and vertical, while others are quite open. These lines are due to
the folding of the strata in consequence of the lateral pressure they
are subjected to, when crowded into the lower course of the valleys, and
the difference in their dip is due to the greater or less force of that
pressure. The wood-cut on the next page represents a transverse cut
across the Lauter-Aar and the Finster-Aar, the two principal tributaries
to the great Aar glacier, and includes also a number of small lateral
glaciers which join them. The beds on the left, which dip least, and are
only folded gently downward, forming very open loops, are those of the
Lauter-Aar, where the lateral pressure is comparatively slight.
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