“It must have been almighty dangerous,” gasped Ted.
“Well, not after we learned the ropes. Sometimes we accidentally put a foot through a thin place and steam came through. I assure you we stepped lively then. At other times our feet sank into the soft, hot mud.
“By the way, there is a mountain across the head of the valley that looks like a crouching dog, and it has been named Cerberus.”
“Were those geysers, those ten thousand smokes?” asked the old prospector.
“No, a geyser comes after volcanic activity, while here something is still likely to happen. A geyser begins as a column of steam and hot water, which erupts as often as the water gets to the boiling point. It follows that the water must accumulate in rock not so hot that it would instantly vaporize it. But the rock underlying this valley is so hot that no water can accumulate.”
“How large are the vents through which the steam comes?” asked Ted.
“All sizes down to nothing at all. There are even a few craters 100 feet across, that have been produced by volcanic explosions. You will find these craters, generally, along a large fissure, just the way you find the Aleutian chain of volcanoes along a fissure in the earth’s crust several hundred miles in length.
“There are fissures all along the margins of the valley, besides those in the center, and many of these have one side standing higher than the other, showing them to be earthquake faults,—the same sort of thing we see here in the rocks of the Sierras. And you should hear the hissing and roaring of the steam as it forces its way up through these fissures from the hot depths beneath. Sometimes it looks like blue smoke, it is so full of gases, especially sulphur dioxide, the gas that is given off by burning sulphur. So the popular notion of Hades isn’t so far off after all, eh?”
“Could you smell the sulphur fumes?”
“Sometimes, yes,—when the other gases did not overwhelm the odor. But the weirdest part of all is the incrustations along the borders of the vents. All colors of the rainbows—shapes as fantastic as anything in fairyland. Lots of yellow, of course, from the sulphur,—crystals of it, some of them neighbor to an orange tinted crystal, lying in the blue mud. It was a beautiful color combination. Then there were green and gray alum crystals which looked like growing lichens. There were also deep green algæ actually growing. Strange how certain designs are used over and over again in nature! In other places the mud is actually burned brick red, especially where the fumaroles are burnt out. This shades to purple, and in other places to pink. But the most surprising, perhaps, were the white vents just tinted with a delicate pink or cream.