n drowned above
Martigny, were afterwards found, at the distance of about thirty miles,
floating on the farther side of the Lake of Geneva, near Vevay.

The waters, on escaping from the temporary lake, intermixed with mud and
rock, swept along, for the first four miles, at the rate of above twenty
miles an hour; and M. Escher, the engineer, calculated that the flood
furnished 300,000 cubic feet of water every second--an efflux which is
five times greater than that of the Rhine below Basle. Now, if part of
the lake had not been gradually drained off, the flood would have been
nearly double, approaching in volume to some of the largest rivers in
Europe. It is evident, therefore, that when we are speculating on the
excavating force which a river may have exerted in any particular
valley, the most important question is, not the volume of the existing
stream, nor the present levels of its channel, nor even the nature of
the rocks, but the probability of a succession of floods at some period
since the time when the valley may have been first elevated above the
sea.

For several months after the dabacle of 1818, the Dranse, having no
settled channel, shifted its position continually from one side to the
other of the valley, carrying away newly-erected bridges, undermining
houses, and continuing to be charged with as large a quantity of earthy
matter as the fluid could hold in suspension. I visited this valley four
months after the flood, and was witness to the sweeping away of a
bridge, and the undermining of part of a house. The greater part of the
ice-barrier was then standing, presenting vertical cliffs 150 feet high,
like ravines in the lava-currents of Etna or Auvergne, where they are
intersected by rivers.

Inundations, precisely similar, are recorded to have occurred at former
periods in this district, and from the same cause. In 1595, for example,
a lake burst, and the waters, descending with irresistible fury,
destroyed the town of Martigny, where from sixty to eighty persons
perished. In a similar flood, fifty years before, 140 persons were
drowned.

_Flood at Tivoli_, 1826.--I shall conclude with one more example derived
from a land of classic recollections, the ancient Tibur, and which,
like all the other inundations above alluded to, occurred within the
present century. The younger Pliny, it will be remembered, describes a
flood on the Anio, which destroyed woods, rocks, and houses, with the
most sumptuous vi