nts of the main valley of the
Rhone, above the Lake of Geneva. Its upper portion was, in 1818,
converted into a lake by the damming up of a narrow pass, by avalanches
of snow and ice, precipitated from an elevated glacier into the bed of
the river Dranse. In the winter season, during continued frost, scarcely
any water flows in the bed of this river to preserve an open channel, so
that the ice barrier remained entire until the melting of the snows in
spring, when a lake was formed above, about half a league in length,
which finally attained in some parts a depth of about two hundred feet,
and a width of about seven hundred feet. To prevent or lessen the
mischief apprehended from the sudden bursting of the barrier, an
artificial gallery, seven hundred feet in length, was cut through the
ice, before the waters had risen to a great height. When at length they
accumulated and flowed through this tunnel, they dissolved the ice, and
thus deepened their channel, until nearly half of the whole contents of
the lake were slowly drained off. But at length, on the approach of the
hot season, the central portion of the remaining mass of ice gave way
with a tremendous crash, and the residue of the lake was emptied in half
an hour. In the course of its descent, the waters encountered several
narrow gorges, and at each of these they rose to a great height, and
then burst with new violence into the next basin, sweeping along rocks,
forests, houses, bridges, and cultivated land. For the greater part of
its course the flood resembled a moving mass of rock and mud, rather
than of water. Some fragments of granitic rocks, of enormous magnitude,
and which from their dimensions, might be compared without exaggeration
to houses, were torn out of a more ancient alluvion, and borne down for
a quarter of a mile. One of the fragments moved was sixty paces in
circumference.[276] The velocity of the water, in the first part of its
course, was thirty-three feet per second, which diminished to six feet
before it reached the Lake of Geneva, where it arrived in six hours and
a half, the distance being forty-five miles.[277]

This flood left behind it, on the plains of Martigny, thousands of trees
torn up by the roots, together with the ruins of buildings. Some of the
houses in that town were filled with mud up to the second story. After
expanding in the plain of Martigny, it entered the Rhone, and did no
farther damage; but some bodies of men, who had bee