24 BOTANICAL INFORMATION. 



and October, when the others of that great family are scarcely 

 over. Gaillardia is the first and the last. All other plants 

 have done blooming about the middle of August. 



An ashy, dull, scanty, green is the prevailing colour in the 

 desert, and an ochre-yellow almost as dull as the drifting 

 sand itself, more so when the Artemisia are in bloom. Vivid 

 hues appear only on firm sandy plains, for a very short series 

 of days, during the latter part of June. In fertile valleys the 

 green is very deep and rich, and the colours reversed, that is, 

 the dull yellow prevails in the spring in different species of 

 Crepis, Sonchus, &c, and the vivid colours about the month 

 of September. All trees and shrubs have grayish foliage, at 

 least, ashy bark, and retain their leaves till the beginning of 

 November. 



1*/ Sub-region. — Highest, cold and firm sandy table-lands, 

 on the depressed central chain of the Rocky Mountains, 

 about the uppermost sources of Missouri River. 



This is the most northern part of the Sierra verra or 

 Green Desert, cold and inhospitable, though less so than 

 the great tracts of sandy desert lower east. A succession of 

 table-lands rise continually and imperceptibly north-westward 

 from the uppermost forks of the Colorado of the west. The 

 narrow valleys also rise at least in the same ratio and expand 

 at the same time to a very great width ; the plains become 

 rock-bound, narrower, and either mountainous, towering, 

 capped with perpetual snow, or more frequently truncated at 

 a considerable height, (about 5000 — 6000 feet of elevation). 

 These plateaux and the extensive valley plains constitute this 

 sub-region. 



In very few localities are the lower strata visible ; the most 

 conspicuous I found about Madison Forks, consisting of a 

 chasm in a great sandy plain, several miles long, showing 

 massive, horizontal strata of a compact smoky-white clay- 

 stone, with a deep blueish fracture, becoming white and 

 dusty when exposed to light : the upper strata were lighter 

 and were overlaid by a thin strata of very heavy black iron- 

 stone, with a close-grained crystalline fracture, and a porose 



