24 PHYSIOGRAPHIC GEOLOGY. 



peculiarities of each dependent on their different relations to the 

 oceans. 



29. (1.) America. — The two Americas are alike in lying between 

 the Atlantic and the Pacific : moreover, South America is set so 

 far to the east of North America (being east of the meridian of 

 Niagara Falls) that each has an almost entire ocean-contour. 

 Moreover, each is triangular in outline, with the widest part, or 

 head, to the north. 



North America, in accordance with the law, has on the Pacific 

 side — the side of the great ocean — the Eocky Mountains, on the 

 Atlantic side the low Appalachians, and between the two there is 

 the great plain of the interior. This is seen in the annexed 

 section (fig. 18) from west to east : on the west, the Eocky Moun- 



Fig. 18. 



ftA\. 



w a i c d v 



tains, with the double crest, at 6, the Washington Eange at a, 

 between a, b the Great Basin, at d the Appalachians, c the Mis- 

 sissippi, 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 sum- 

 mits than the crest-ridges of the Rocky chain. In the former there is a line 

 of snowy cones from 12,000 to 16,000 or 18,000 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, south, Mount 

 Hood, Mount Pitt, Mount Jefferson, and the Shasta Peak, — the last on the border 

 of California. Still nearer the sea there is what is called the Coast Range, con- 

 sisting 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 

 6700 feet, and are in general under 2500 feet. 



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

 much encumbered with land ; and, correspondingly, there is no 

 distinct mountain-chain facing the ocean. The mountains of 

 Greenland are an independent 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 ; 



