But if
not, sooner or later, it bores up through the new sedimentary rocks,
faulting them by earthquake shocks till it gets free vent, and begins
its layers of alternate ash and lava once more.
And consider this fact also: If near the first (as often happens)
there is another volcano, the lava from one may run over the lava
from the other, and we may have two lavas of different materials
overlying each other, which have come from different directions. The
ashes blown out of the two craters may mingle also, and so, in the
course of ages, the result may be such a confusion of ashes, lavas,
and sedimentary rocks as we find throughout most mountain ranges in
Snowdon, in the Lake mountains, in the Auvergne in France, in Sicily
round Etna, in Italy round Vesuvius, and in so many West Indian
Islands; the last confusion of which is very likely to be this:
That when the volcano has succeeded--as it did in the case of Sabrina
Island off the Azores in 1811, and as it did, perhaps often, in
Snowdonia--in piling up an ash cone some hundred feet out of the sea;
that--as has happened to Sabrina Island--the cone is sunk again by
earthquakes, and gnawn down at the same time by the sea-waves, till
nothing is left but a shoal under water. But where have all its vast
heaps of ashes gone? To be spread about over the bottom of the sea,
to mingle with the mud already there, and so make beds of which, like
many in Snowdon, we cannot say whether they are of volcanic or of
marine origin, because they are of both.
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