For of the inside of this
earth we know nothing whatsoever: we only know that it is, on an average,
several times as heavy as solid rock; but how that can be, we know not.
So let us look at the chimney, and what comes out of it; for we can see
very little more.
Why is a volcano like a cone?
For the same cause for which a molehill is like a cone, though a very
rough one; and that the little heaps which the burrowing beetles make on
the moor, or which the ant-lions in France make in the sand, are all
something in the shape of a cone, with a hole like a crater in the
middle. What the beetle and the ant-lion do on a very little scale, the
steam inside the earth does on a great scale. When once it has forced a
vent into the outside air, it tears out the rocks underground, grinds
them small against each other, often into the finest dust, and blasts
them out of the hole which it has made. Some of them fall back into the
hole, and are shot out again: but most of them fall round the hole, most
of them close to it, and fewer of them farther off, till they are piled
up in a ring round it, just as the sand is piled up round a beetle's
burrow. For days, and weeks, and months this goes on; even it may be for
hundreds of years: till a great cone is formed round the steam vent,
hundreds or thousands of feet in height, of dust and stones, and of
cinders likewise. For recollect, that when the steam has blown away the
cold earth and rock near the surface of the ground, it begins blowing out
the hot rocks down below, red-hot, white-hot, and at last actually
melted.
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