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.