On leaving us yesterday he pursued his route along the foot of the hills, which he ascended at the distance of eight miles; from these the wide plains watered by the Missouri and the Yellowstone spread themselves before the eye, occasionally varied with the wood of the banks, enlivened by the irregular windings of the two rivers, and animated by vast herds of buffaloe, deer, elk, and antelope.  The confluence of the two rivers was concealed by the wood, but the Yellowstone itself was only two miles distant to the south.  He therefore descended the hills and encamped on the bank of the river, having killed as he crossed the plain four buffaloes; the deer alone are shy and retire to the woods, but the elk, antelope, and buffaloe suffered him to approach them without alarm, and often followed him quietly for some distance.  This morning he sent a man up the river to examine it, while he proceeded down to the junction:  the ground on the lower side of the Yellowstone near its mouth, is flat, and for about a mile seems to be subject to inundation, while that at the point or junction, as well as on the opposite side of the Missouri, is at the usual height of ten or eighteen feet above the water, and therefore not overflown.  There is more timber in the neighbourhood of this place, and on the Missouri, as far below as the Whiteearth river, than on any other part of the Missouri on this side of the Chayenne:  the timber consists principally of cottonwood, with some small elm, ash, and box alder.  On the sandbars and along the margin of the river grows the small-leafed willow; in the low grounds adjoining are scattered rosebushes three or four feet high, the redberry, serviceberry and redwood.  The higher plains are either immediately on the river, in which case they are generally timbered, and have an undergrowth like that of the low grounds, with the addition of the broad-leafed willow, gooseberry, chokecherry, purple currant, and honeysuckle; or they are between the low grounds and the hills, and for the most part without wood or any thing except large quantities of wild hysop; this plant rises about two feet high, and like the willow of the sandbars is a favourite food of the buffaloe, elk, deer, grouse, porcupine, hare, and rabbit.  This river which had been known to the French as the Roche jaune, or as we have called it the Yellowstone, rises according to Indian information in the Rocky mountains; its sources are near those of the Missouri and the Platte, and it may be navigated in canoes almost to its head.  It runs first through a mountainous country, but in many parts fertile and well timbered; it then waters a rich delightful land, broken into vallies and meadows, and well supplied with wood and water till it reaches near the Missouri open meadows and low grounds, sufficiently timbered on its borders.  In the upper country its course is represented as very rapid, but during the two last and largest portions, its current is much more gentle than that of the Missouri, which it resembles also