24 PHYSIOGRAPHIC GEOLOGY. 



Fig. 18. 



crest, at b ; the Washington range at a ; between a b the Great Basin ; 

 at d the Appalachians; c the Mississippi; and between d and b a section 

 of the Mississippi river-system. 



The Cascade and Nevada ranges are even more lofty in some of their summits than 

 the crest-ridges of the Rocky chain. In the former there is a line of snowy cones from 

 10,000 to nearly 14,500 feet in elevation, including Mount Baker, near Puget's Sound, 

 and, to the south of this, Mount St. Helen's, Mount Adams, and Mount Rainier, north 

 of the Columbia, and, soulh, Mount Hood, Mount Pitt, Mount Jefferson, and the Shasta 

 Peak, — the last 14,440 feet, according to Whitney. Still nearer the sea, there is what 

 is called the Coast Range, consisting of lower elevations. Between the two lie the 

 valley of the Sacramento and Joaquin, in California, and that of the Willamette, in 

 Oregon. 



The Appalachians, on the east, reach an extreme height of but 6,700 

 feet, and are in general under 2,500 feet. 



To the north of North America lies the small Arctic Ocean, much 

 encumbered with land ; and, correspondingly, there is no distinct moun- 

 tain-chain facing the ocean. The mountains of Greenland are an in- 

 dependent system, pertaining to that semi-continent by itself. 



The characteristics of the interior plain of the continent are well 

 displayed in its river-systems : the great Mississippi system turned to 

 the south, and making its exit into the Gulf of Mexico between the 

 approaching extremities of the eastern and western mountain-ranges ; 

 the St. Lawrence sloping off northeastward ; the Mackenzie, to the 

 northward ; the central area of the plain dividing the three systems 

 being only about 1,700 feet above the ocean, — a less elevation than 

 about the head-waters of the Ohio in the State of New York. 



South America, like North America, has its great western range of 

 mountains, and its smaller eastern (Fig. 19) ; and the Brazilian line (b) 



Fig. 19. 



A. 



w 



is closely parallel to that of the Appalachians. As the Andes (a) face 

 the South Pacific, a wider and probably much deeper ocean than the 

 North Pacific, so they have more than twice the average height of the 

 Rocky Mountains, and, moreover, they rise more abruptly from the 

 ocean, with narrow shore-plains. 



