a round cup. You may prove for yourself that it must be so, if you will
try. Do you not know that if you dig a round hole in the ground, and
leave it to crumble in, it is sure to become cup-shaped at last, though
at first its sides may have been quite upright, like those of a bucket?
If you do not know, get a trowel and make your little experiment.

And now you ought to understand what "cone" and "crater" mean. And more,
if you will think for yourself, you may guess what would come out of a
volcano when it broke out "in an eruption," as it is usually called.
First, clouds of steam and dust (what you would call smoke); then volleys
of stones, some cool, some burning hot; and at the last, because it lies
lowest of all, the melted rock itself, which is called lava.

And where would that come out? At the top of the chimney? At the top of
the cone?

No. Madam How, as I told you, usually makes things make themselves. She
has made the chimney of the furnace make itself; and next she will make
the furnace-door make itself.

The melted lava rises in the crater--the funnel inside the cone--but it
never gets to the top. It is so enormously heavy that the sides of the
cone cannot bear its weight, and give way low down. And then, through
ashes and cinders, the melted lava burrows out, twisting and twirling
like an enormous fiery earth-worm, till it gets to the air outside, and
runs off down the mountain in a stream of fire. And so you may see (as
are to be seen on Vesuvius now) two eruptions at once--one of burning
stones above, and one of melted lava below.

And what is lava?