Meeting with wood at about three o'clock P. M., we resolved to encamp. On the two preceding evenings, we had found it difficult to collect as much wood as sufficed to kindle a fire, which was afterwards kept up with the dung of the bison, though not without some difficulty, as the weather was rainy.
The dung of the bison is used as fuel in many parts of the woodless country southwest of the Missouri, by the Indians, and by hunters, who often encamp where no wood is to be found. We learn from Sonnini[106] and others, that the excrement of the camel, mixed with chopped straw and afterwards dried, is similarly used in the woodless parts of Egypt.
The hills on the south side of the Platte, above the confluence of the north fork, become more abrupt and elevated, approaching in character those of the Missouri which are destitute of stone. There is here the same transcript of Alpine scenery, in miniature, which constitutes so striking a feature in the Missouri landscape, when viewed from the river bottom.
We had no sooner crossed the Platte, than our attention was arrested by the beautiful white primrose (œnothera pinnatifida, N.) with its long and slender corolla reclining upon the grass. The flower, which is near two inches long, constitutes about one-half of the entire length of the plant.[107]
The valley of the Platte, above the forks, is much narrower, and a little more irregular in direction than below, and is frequently interrupted by small hills running in towards the river. On ascending these hills, we found them of a coarse sand, and containing more gravel and small pebbles than below. Among the gravel stones, small fragments of flesh-coloured {155} felspar are distinguished. About the summits of the hills we saw some detached pieces of fine carnelion, with agates and calcedony.
We had often examined, with some anxiety, the turbid waters of the Platte, hoping thereby to gain information respecting the predominating rock formations of the mountainous district, from which that river descends.
It had been a received opinion among some of the geologists of the United States, that the Rocky Mountains were not of primitive rocks; we had hitherto observed nothing which could either confirm or invalidate this opinion.
The great alluvial formation, which occupies the country on both sides of the lower portion of the river Platte, is an almost unmixed siliceous sand, in no manner distinguishable from the débris of the sandstones of transition mountains. Near the forks of the Platte, we first observed that the waters of that river bring down, among other matters, numerous small scales of mica. This also is a constituent of the sandstones of the lower secondary or transition formations. The fragments of unmixed and crystalline felspar, which now began to be of frequent occurrence, were considered as the first convincing evidence of the primitive character of the Rocky Mountains. These fragments of felspar, we believed, could have been derived from no other than primitive rocks.
During all the day on the 23d we travelled along the south side of the Platte, our course inclining something more towards the south-west than heretofore.
Intermixed in the narrow fringe of timber, which marks the course of the river, are very numerous trees, killed by the action of the beaver or by the effects of old age; their decorticated and bleached trunks and limbs strongly contrasting with the surrounding objects, many of them rendered doubly {156} interesting by affording a support to the nests of the bald eagle, elevated like a beacon in the horizon of the traveller.