This detachment left the camp before sunrise, and taking the most direct route across the plains, arrived at eleven o'clock at the base of the mountain. Here Lieutenant Swift found a place suited to his purpose; where, also, was a convenient spot for those who were to ascend the mountain to leave their horses. At this place was a narrow, woodless valley, dividing transversely several sandstone ridges, and extending westward to the base of the peak. After establishing their horse-camp, the detachment moved up the valley on foot, arriving about noon at the boiling spring, where they dined on a saddle of venison, and some bison ribs they had brought ready cooked from camp. The _boiling spring_ is a large and beautiful fountain of water, cool and transparent, and aërated with carbonic acid. It rises on the brink of a small stream, which here descends from the mountain, at the point where the bed of this stream divides the ridge of sandstone which rests against the base of the first {213} granitic range. The water of the spring deposits a copious concretion of carbonate of lime,[2] which has accumulated on every side, until it has formed a large basin overhanging the stream; above which it is raised several feet. This basin is of a snowy whiteness, and large enough to contain three or four hundred gallons, and is constantly overflowing. The spring rises from the bottom of the basin, with a rumbling noise, discharging about equal volumes of air and of water, probably about fifty gallons per minute; the whole kept in constant agitation. The water is beautifully transparent; and has the sparkling appearance, the grateful taste, and the exhilarating effect, of the most highly aërated artificial mineral waters. Distant a few rods from this is another spring of the same kind, which discharges no water, its basin remaining constantly full, and air only escaping from it. We collected some of the air from both these springs in a box we had carried for the reception of plants; but could not perceive it to have the least smell, or the power of extinguishing flame, which was tested, by plunging into it lighted splinters of dry cedar. The temperature of the water of the larger spring at noon was 63°, the thermometer at the same time, in the shade, stood at 68°; immersed in the small spring, at 67°. This difference in temperature is owing to the difference of situation, the higher temperature of the small spring depending entirely on its constant exposure to the rays of the sun, and to its retaining the same portion of water; while that in the large spring is constantly replaced by a new supply.[3] After we had dined, and hung up some provisions in a large red cedar-tree near the spring, intending it for a supply on our return, we took leave of Lieutenant Swift, and began to ascend the mountain. We carried with us each a small blanket, ten {214} or twelve pounds of bison meat, three gills of parched corn meal, and a small kettle.