Rocky Mountains. 475 



the traveller, who winds his way amongst them, and are en- 

 entirely destitute of grass, their surface being covered with 

 a deep dust. Until recently, we had no opportunity to ob- 

 serve 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 in- 

 dulges 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 undulat- 

 ing or broken surface, are almost exclusively occupied by a 

 scattered growth of several species of wormwood, (Artemi- 

 sia.) 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* 

 A. cernaa, A. canadensis ; most of these species have sim- 

 ple 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. 



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 withloose and fine 

 sand, blown from the adjacent hills. In the low plains along 



* A. Columhiensis. This is said to be the plant known to the party of 

 Le" is and Clark, by the name of " wild sa^e." It occurs abundantly 

 iu the barren plains of the Columbia river, where it furnishes the sole ar- 

 ticle of fuel or of shelter, to the Indians, who wander in those woodless de- 

 serts. See Nuttall's Genera, vol. li. p. 14?. 



