No. 543] 



NOTES AND LITERATURE 



177 



The western third of the continent is much more varied in its 

 topography than the Atlantic side, and shows a correspondingly 

 greater richness and diversity in its flora, since the climatic dif- 

 ferences, due to the extremely varied topography, are much 

 greater than is the case in the eastern states. 



Rising abruptly from the plains, the Rocky Mountains form 

 the beginning of the great complex of mountains and deserts 

 that stretches to the Pacific Coast. Unlike the worndown Appa- 

 lachian system, the western mountains arc extremely rugged, 

 and their much greater elevation, rising above the level of per- 

 petual snow, permits of a true Alpine flora. The region bor- 

 dering on the great plains is arid and semi-arid, and lias a pro- 

 nounced continental climate, with great extremes of heat and 

 cold and a scanty rainfall. 



The lower elevations are mostly destitute of forests except 

 along the water courses and in sheltered canons. Higher up the 



thousand feet a fairly heavy forest is found, in many places 

 composed mainly of coniferous trees. Of these the most im- 

 portant are the Rocky Mountain Yellow-Pine, the Douglas Fir, 

 the Lodge-pole Pine and Engelmann Spruce. At the lower ele- 

 vations where trees are found they are mostly of Eastern species, 

 some of which, like the White Elm and Cottonwood, are found 

 sparingly as far west as the base of the Rockies. 



For the most part, however, the Rocky Mountain flora is allied 

 to that of the Pacific Coast and the arid southwestern region 

 whose plants are mainly of Mexican origin. A marked feature 

 of the eastern Rocky Mountains is the formation oi beautitul 

 glacial parks, which are especially well developed in Colorado. 

 The floors of these parks are covered with a rich carpet of grasses 



