A large and beautiful animal[25] of the lizard kind (belonging to the genus ameiva) was noticed in this day's ride. It very much resembles the lacerta ameiva, as figured and described by Lacepede,[26] but the tail is proportionably much longer. Its movements were so extremely rapid that it was with much difficulty we were able to capture a few of them. {239} We had proceeded about eight or ten miles from our camp, when we observed a very considerable change in the character both of the river and its valley, the former becoming wider, less rapid, and filled with numerous islands; the latter bounded by sloping sandhills, instead of perpendicular precipices. Here the barren cedar-ridges, formerly mentioned, are succeeded by still more desolate plains, with scarce a green or a living thing upon them, except here and there a tuft of grass, an orbicular lizard, basking on the scorching sand, a solitary pimelia, a blaps, or a galeodes. Among the few stinted and withered grapes, we distinguished a small cespitose species of agrestis, and several others which are thought to be undescribed. Near the river, and in spots of uncommon fertility, the unicorn plant, (martynia proboscidea, Ph.) was growing in considerable perfection. This plant, which is sometimes cultivated in the gardens, where it is known by the name of cuckold's horns, is a native of the Platte and Arkansa, and is occasionally seen in every part of the open country from St. Louis westward to the mountains. A little before noon, we crossed a small stream which was called Castle Rock creek, from a remarkable pile of naked rocks, and halted for dinner on the bank of the river.[27] In the morning, Mr. Peale and two hunters had taken a different route from the remainder of the party, hoping to meet with game. They arrived at a small grove of timber, where it was thought deer might be found; they therefore left their horses in care of one of the hunters, and entered the wood on foot. The man had been left alone but a short time, when he discovered a large grizzly bear (ursus horribilis, Ord.) approaching rapidly towards him, and without staying to make any inquiry into the intentions of the animal, mounted his horse and fled. This animal is widely distinct from any known {240} species of bear, by the essential character of the elongated anterior claws, and rectilinear or slightly arcuated figure of its facial profile. In general appearance it may be compared to the alpine bear, (U. arctus), and particularly to the Norwegian variety. The claws, however, of these appear to be of the usual form and not elongated, and the facial space included between the eyes is deeply indented; they also differ in their manners, and climb trees, which the grizzly bear is never known to do.