This is Cotopaxi, in Quito, more than 19,000 feet in height.

All those sloping sides are made of cinders and ashes, braced together, I suppose, by bars of solid lava-stone inside, which prevent the whole from crumbling down.

The upper part, you see, is white with snow, as far down as a line which is 15,000 feet above the sea; for the mountain is in the tropics, close to the equator, and the snow will not lie in that hot climate any lower down.

But now and then the snow melts off and rushes down the mountain side in floods of water and of mud, and the cindery cone of Cotopaxi stands out black and dreadful against the clear blue sky, and then the people of that country know what is coming.
The mountain is growing so hot inside that it melts off its snowy covering; and soon it will burst forth with smoke and steam, and red-hot stones and earthquakes, which will shake the ground, and roars that will be heard, it may be, hundreds of miles away.
And now for the words cone, crater, lava.

If I can make you understand those words, you will see why volcanos must be in general of the shape of Cotopaxi.
Cone, crater, lava: those words make up the alphabet of volcano learning.
The cone is the outside of a huge chimney; the crater is the mouth of it.
The lava is the ore which is being melted in the furnace below, that it may flow out over the surface of the old land, and make new land instead.
And where is the furnace itself?
Who can tell that?
Under the roots of the mountains, under the depths of the sea; down "the path which no fowl knoweth, and which the vulture's eye hath not seen: the lion's whelp hath not trodden it, nor the fierce lion passed by it.