In course of time the source of sulphurous acid becomes exhausted, and sulphuretted hydrogen alone remains active. The acid reaction of the soil disappears, yielding to an alkaline reaction by the formation of sulphids. At the same time carbonic acid begins to act upon the rocks, and the alkaline bi-carbonates thus produced dissolve the silica, which on the evaporation of the water is deposited in the form of opal or quartz or silicious earth, and thus the shell of the springs is formed, on the structure of which the periodicity of the outburst depends.... The deposition of silica in quantities sufficient for the formation of this spring-apparatus in the course of years, takes place only in the alkaline springs. Their water is either neutral or has a slightly alkaline reaction. Silica, common salt, carbonates and sulphates are the chief ingredients dissolved in it. In the place of sulphurous acid the odor of sulphuretted hydrogen is sometimes observed in these springs.... By the gradual cooling of the volcanic rocks under the surface of the earth the hot springs themselves gradually die out, for they too are but a transient phenomenon in the eternal change of created things."
On the day that I found myself separated from the company, and for several days previous, our course had been impeded by the dense growth of pine forest, and occasional large tracts of fallen timber frequently rendering our progress almost impossible. Whenever we came to one of these immense windfalls, each man engaged in the pursuit of a passage through it, and it was while thus employed, and with the idea that I had found one, that I strayed out of sight and hearing of my comrades. We had had a toilsome day. It was quite late in the afternoon. As separations like these had frequently occurred, it gave me no alarm, and I rode on, fully confident of soon rejoining the company, or of finding their camp. I came up with the pack-horse, which Mr. Langford afterwards recovered, and tried to drive him along. But failing to do so, and my eyesight being defective, I spurred forward, intending to return with assistance from the party. This incident tended to accelerate my speed. I rode on in the direction which I supposed had been taken, until darkness overtook me in the dense forest. This was disagreeable enough, but caused me no alarm. I had no doubt of being with the party at breakfast the next morning. I selected a spot for comfortable repose, picketed my horse, built a fire, and went to sleep.