ses, which boils up through
the sea, and forms a cloud above; that cloud descends again in heavy
rain, and gives out often true lightning from its under side.

But it does more. It acts as a true steam-gun, hurling into the air
fragments of cold rock rasped off from the sides of the bore, and
fragments also of melted lava, and clouds of dust, which fall again
into the sea, and form there beds either of fine mud or of breccia--
that is, fragments of stone embedded in paste. This, the reader will
understand, is no fancy sketch, as far as I am concerned. I have
steamed into craters sawn through by the sea, and showing sections of
beds of ash dipping outwards and under the sea, and in them boulders
and pebbles of every size, which had been hurled out of the crater;
and in them also veins of hardened lava, which had burrowed out
through the soft ashes of the cone. Of those lava veins I will speak
presently. What I want the reader to think of now is the immense
quantity of ash which the steam-mitrailleuse hurls to so vast a
height into the air, that it is often drifted many miles down to
leeward. To give two instances: The jet of steam from Vesuvius, in
the eruption of 1822, rose more than four miles into the air; the jet
from the Souffriere of St. Vincent in the West Indies, in 1812,
probably rose higher; certainly it met the N.E. trade-wind, for it
poured down a layer of ashes, several inches thick, not only on St.
Vincent itself, but on Barbadoes, eighty miles to windward, and
therefore on all the sea between. Now let us consider what that
represents--a layer of fine mud, laid down at the bottom of the
ocean, several inches thick, eighty miles at least long, and twenty
miles perhaps broad, by a single eruption. Suppose that hardened in
long ages (as it would be under pressure) into a bed of fine grained
Felstone, or volcanic ash; and we can understand how the ash-beds of
Snowdonia--which may be traced some of them for many square miles--
were laid down at the bottom of an ancient sea.

But now about the lavas or true volcanic rocks, which are painted (as
is usual in geological maps) red. Let us go down to the bottom of
the sea, and build up our volcano towards the surface.

First, as I said, the subterranean steam would blast a bore. The
dust and stones, rasped and blasted out of that hole would be spread
about the sea-bottom as an ash-bed sloping away round the hole; then
the