by observations on certain effects of lava flows from Vesuvius. The
writer was informed by a very judicious observer, a resident of
Naples, who had interested himself in the phenomena of that volcano,
that the lava streams when they penetrated a cistern, such as they
often encounter in passing over villages or farmsteads, vaporized the
water, and gave rise, through the action of the steam, to small
temporary cones, which, though generally washed away by the further
flow of the liquid rock, are essentially like those which we find on
Ætna. Such subsidiary, or, as they are sometimes called, parasitic
cones, are known about other volcanoes, but nowhere are they so
characteristic as on the flanks of that wonderful volcano.

A very conspicuous feature in the Ætnean cone consists of a great
valley known as the Val del Bove, or Bull Hollow, which extends from
the base of the modern and ever-changeable cinder cone down the flanks
of the older structure to near its base. This valley has steep sides,
in places a thousand or more feet high, and has evidently been formed
by the down-settling of portions of the cone which were left without
support by the withdrawal from beneath them of materials cast forth in
a time of explosion. In an eruption this remarkable valley was the
seat of a vast water flood, the fluid being cast forth from the crater
at the beginning of the explosion. In the mouths of this and other
volcanoes, after a long period of repose, great quantities of water,
gathering from rains or condensed from the steam which slowly escapes
from these openings, often pours like a flood down the sides of the
mountains. In the great eruption of Galongoon, in Java, such a mass of
water, cast forth by a terrific explosion, mingled with ashes, so that
the mass formed a thick mud, was shot forth with such energy that it
ravaged an area nearly eighty miles in diameter, destroying the
forests and their wild inhabitants, as well as the people who dwelt