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 molten lava would rise in the bore, and flow out over the ashes
and the sea-bottom--perhaps in one direction, perhaps all round.
Then, usually, the volcano, having vented itself, would be quieter
for a time, till the heat accumulated below, and more ash was blasted
out, making a second ash-bed; and then would follow a second lava
flow.
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