egard the late catastrophe as portentous. We may,
at least, recommend the modern votaries of the goddess to lose no time
in making a pilgrimage to her shrine, for the next flood may not respect
the temple.

_Excavation of rocks by running water._--The rapidity with which even
the smallest streams hollow out deep channels in soft and destructible
soils is remarkably exemplified in volcanic countries, where the sand
and half-consolidated tuffs opposed but a slight resistance to the
torrents which descend the mountain-side. After the heavy rains which
followed the eruption of Vesuvius in 1824, the water flowing from the
Atrio del Cavallo cut, in three days, a new chasm through strata of tuff
and ejected volcanic matter, to the depth of twenty-five feet. I found
the old mule-road, in 1828, intersected by this new ravine.

The gradual erosion of deep chasms through some of the hardest rocks, by
the constant passage of running water, charged with foreign matter, is
another phenomenon of which striking examples may be adduced.
Illustrations of this excavating power are presented by many valleys in
central France where the channels of rivers have been barred up by solid
currents of lava, through which the streams have re-excavated a passage,
to the depth of from twenty to seventy feet and upwards, and often of
great width. In these cases there are decisive proofs that neither the
sea, nor any denuding wave or extraordinary body of water, has passed
over the spot since the melted lava was consolidated. Every hypothesis
of the intervention of sudden and violent agency is entirely excluded,
because the cones of _loose_ scoriae, out of which the lavas flowed, are
oftentimes at no great elevation above the rivers, and have remained
undisturbed during the whole period which has been sufficient for the
hollowing out of such enormous ravines.

_Recent excavation by the Simeto._--But I shall at present confine
myself to examples derived from events which have happened since the
time of history.

[Illustration: Fig. 16.

Recent excavation of lava at the foot of Etna by the river Simeto.]

At the western base of Etna, a current of lava (A A, fig. 16),
descending from near the summit of the great volcano, has flowed to the
distance of five or six miles, and then reached the alluvial plain of
the Simeto, the largest of the Sicilian rivers, which skirts the base of
Etna, and falls into the sea a few miles south of Catania. The lava
en