At Rossberg, for instance, in the
Canton of Schwitz, the land-slide which buried the village of Goldau
under a terrific avalanche, and filled a part of the Lake of Lauertz,
spread an immense number of huge boulders across the valley, some of
which even rolled up the opposite side to a considerable height. Many of
these boulders might easily be mistaken for erratic boulders, were not
the aggregate of these loose materials traceable to the hills from which
they descended. In this case water had no part in loosening or bringing
down this mass of fragments. They simply rolled from the declivity, and
stopped when they had exhausted the momentum imparted to them by their
weight. In the case of the _debacle_ of Bagnes, above Martigny, in a
valley leading to the St. Bernard, the circumstances were very
different. A glacier, advancing beyond its usual limits and rising
against the opposite mountain-slope, dammed up the waters of the torrent
and caused a lake to be formed. The obstruction gave way in the course
of time, and the waters of the lake rushed out, carrying along with
them huge boulders and a mass of loose materials of all sorts, and
scattering them over the plain below. Such an accumulation of _debris_
differs from the pebbles and loose fragments found in river-beds.
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