We have frequently remarked broad shallow excavations in the soil, of the diameter of from five to eight feet, and greatest depth from six inches to eighteen. These are of rare occurrence near the Missouri, as far as Engineer cantonment, and in other districts where the bison is seldom seen at the present day; and when they do exist there, they are overgrown by grass and nearly obliterated. As you approach the country, still the constant residence of these animals, the excavations become more numerous, and are less productive of grass. They now are so numerous as to be of constant recurrence, offering a considerable impediment to the traveller, who winds his way amongst them, and are entirely destitute of grass, their surface being covered with a deep dust. Until recently, we had no opportunity to observe the cause which gives rise to these appearances; but we were now convinced that they were the result of the habit which the bulls have, in common with the domestic bull, of scraping up the earth with their fore feet, in the process of dusting themselves: they serve also as places for rolling and wallowing; a gratification which the bison bull indulges in as frequently, and in the same manner as the horse. Some extensive tracts of land along the Platte, particularly those portions which are a little elevated, with an undulating or broken surface, are almost exclusively occupied by a scattered growth of several species of wormwood, (artemisia) some of which are common to this country, and that on the lower Missouri: we may enumerate the following—A. ludoviciana, A. longifolia, A. serrata, A. columbiensis,[114] {162} A. cernua, A. canadensis; most of these species have simple or finely divided compound leaves, which are long and slender, and canescent, like those of the A. absynthium, the common wormwood of the gardens. The peculiar aromatic scent, and the flavor of this well known plant, is recognized in all the species we have mentioned. Several of them are eaten by the bisons, and our horses were sometimes reduced to the necessity of feeding upon them. [114] A. columbiensis. This is said to be the plant known to the party of Lewis and Clarke, by the name of "wild sage." It occurs abundantly in the barren plains of the Columbia river; where it furnishes the sole article of fuel or of shelter to the Indians who wander in those woodless deserts. See Nuttall's Genera, vol. ii. p. 142.—JAMES. The intense reflection of light and heat from the surface of many tracts of naked sand, which we crossed, added much to the fatigue and suffering of our journey. We often met with extensive districts covered entirely with loose and fine sand blown from the adjacent hills. In the low plains along the river, where the soil is permanent, it is highly impregnated with saline substances, and too sterile to produce any thing except a few stinted carices and rushes.