"About a hundred yards distant we discovered a boiling alum spring, surrounded with beautiful crystals, from the border of which we gathered a quantity of alum, nearly pure, but slightly impregnated with iron. The violent ebullition of the water had undermined the surrounding surface in many places, and for the distance of several feet from the margin had so thoroughly saturated the incrustation with its liquid contents, that it was unsafe to approach the edge. As one of our company was unconcernedly passing near the brink, the incrustation suddenly sloughed off beneath his feet. A shout of alarm from his comrades aroused him to a sense of his peril, and he only avoided being plunged into the boiling mixture by falling suddenly backward at full length upon the firm portion of the crust, and rolling over to a place of safety. His escape from a horrible death was most marvellous, and in another instant he would have been beyond all human aid. Our efforts to sound the depths of this spring with a pole thirty-five feet in length were fruitless." The report of the Geological Expedition describes these curious springs somewhat more minutely. The first that attracted Dr. Hayden's attention was the powerful steam-vent above mentioned, which he calls the Locomotive Jet. "The aperture is about six inches in diameter, a sort of raised chimney, and all around are numerous small continuous steam-vents, all of which are elegantly lined with the bright-yellow sulphur. The entire surface is covered with the white silicious crust, which gives forth a hollow sound beneath the tread; and we took pleasure in breaking it up in the vicinity of the vents, and exposing the wonderful beauty of the sulphur-coating on the inner sides. This crust is ever hot, and yet so firm that we could walk over it anywhere. On the south side of these hills, close to the foot, is a magnificent sulphur-spring. The deposits around it are silica; but some places are white, and enamelled like the finest porcelain. The thin edges of the nearly circular rim extend over the waters of the basin several feet, yet the open portion is fifteen feet in diameter. The water is in a constant state of agitation. The steam that issues from this spring is so strong and hot that it was only on the windward side that I could approach it and ascertain its temperature, 197°. The agitation seemed to affect the entire mass, carrying it up impulsively to the height of four feet. It may be compared to a huge caldron of perfectly clear water somewhat superheated. But it is the decorations about this spring that lent the charm, after our astonishment at the seething mass before us--the most beautiful scolloping around the rim, and the inner and outer surface covered with a sort of pearl-like bead work. The base is the pure white silica, while the sulphur gave every possible shade, from yellow to the most delicate cream. No kind of embroidering that human art can conceive or fashion could equal