while the
decomposition to which they owe their separation from the solid rock is
often still going on. Such _debris_ are found everywhere about
disintegrating rocks, and they constantly mingle with the loose
fragments brought from a distance by various agencies. They are found
upon and among the glacier-worn pebbles, especially where the latter
have themselves been disturbed since their accumulation. They are also
found among water-worn pebbles, wherever the rocky beds of our rivers or
the rocky bluffs of our sea-shores crumble down. In investigating the
character of loose materials transported from greater or less distances,
either by the agency of glaciers or by water-currents, it is important
at the very outset to discriminate between these deposits of older date
and the local accessions mingling with them.

Occasionally we may have also to distinguish between all these deposits
and the _debris_ brought down by land-slides, or by sudden freshets
transporting to a distance a vast amount of loose materials which are
neither ice-worn nor water-worn. 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. The
comparatively short distance over which they are carried, and the
suddenness of the transportation, all