A large undescribed species of the gaura is common {265} about the banks of all the creeks we had seen since leaving the Arkansa. It attains, ordinarily, the size of G. biennis, but is clearly distinct both from that and all other North American species. It has a broader leaf than any other of the genus met with in this country. The flowers are small, of a purple colour, and incline to form a terminal spike. The whole plant is covered with a dense silky pubescence, and is remarkably soft to the touch. We propose to call it gaura mollis. After travelling one mile and a half into the plain in a due south course, we halted to take the bearings of several remarkable points. Due east was a solitary and almost naked pile of rocks towering to a great elevation above the surface of the plain. James's Peak bore north 71° west; the west Spanish Peak, south 87°. West magnetic variation, 13½ deg. east. As we proceeded, we were surprised to witness an aspect of unwonted verdure and freshness in the grasses and other plants of the plains, and in searching for the cause of this change, we discovered we had arrived at a region differing both in point of soil and geological features from any portion of the country we had before seen. Several circumstances had induced us to conjecture that rocks of the newest fletz trap formation, existed in some portions of the secondary region along the eastern declivity of the Rocky Mountains; but until this time we had met with no positive confirmation of the opinion. We are glad to be at length relieved from the tiresome sameness of the sand formation, and promised ourselves in the treasures of a new and more fertile variety of soil, the acquisition of many important plants. At five P. M. we met with a little stagnant water, near which we encamped, having travelled about ten miles nearly due south from the point where we had left the valley of the creek. The hunters went out on foot in pursuit of bisons, several herds being {266} in sight; but returned at dark, having effected no more than to break the shoulder of a young bull, who ran off, pursued by a gang of wolves. Several of the party understanding the route the animal had taken, and instigated in common with the wolves by the powerful incitement of hunger, resolved to join the chase, and to dispute with their canine competitors the possession of the prey. When they had nearly overtaken the bison, they saw him several times thrown to the ground by the wolves, and afterwards regaining his feet. They soon came near enough to do execution with their pistols, and frightened away the wolves only to make a speedier end of the harassed animal. It was now past nine o'clock, but the starlight was sufficient to enable them to dress the meat, with which they returned loaded to camp, and spent the greater part of the night in regaling on the choice pieces.