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.  But these, as they are hurled into the cool air above, become ashes, cinders, and blocks of stone again, making the hill on which they fall bigger and bigger continually.  And thus does wise Madam How stand in no need of bricklayers, but makes her chimneys build themselves.

And why is the mouth of the chimney called a crater?

Crater, as you know, is Greek for a cup.  And the mouth of these chimneys, when they have become choked and stopped working, are often just the shape of a cup, or (as the Germans call them) kessels, which means kettles, or caldrons.  I have seen some of them as beautifully and exactly rounded as if a cunning engineer had planned them, and had them dug out with the spade.  At first, of course, their sides and bottom are nothing but loose stones, cinders, slag, ashes, such as would be thrown out of a furnace.  But Madam How, who, whenever she makes an ugly desolate place, always tries to cover over its ugliness, and set something green to grow over it, and make it pretty once more, does so often and often by her worn-out craters.  I have seen them covered with short sweet turf, like so many chalk downs.  I have seen them, too, filled with bushes, which held woodcocks and wild boars.  Once I came on a beautiful round crater on the top of a mountain, which was filled at the bottom with a splendid crop of potatoes.  Though Madam How had not put them there herself, she had at least taught the honest Germans to put them there.  And often Madam How turns her worn-out craters into beautiful lakes.  There are many such crater-lakes in Italy, as you will see if ever you go there; as you may see in English galleries painted by Wilson, a famous artist who died before you were