GENERAL FEATURES OF THE EARTH. 



17 



the ordinary maps, but a vast yet gentle swell 

 of the surface, having a base 1000 miles in 

 breadth, and the slopes diversified with va- 

 rious mountain-ridges or spreading out in 

 plateaus at different levels. 



The annexed section (Fig. 2) of the Eocky 

 Mountains along the parallels 41° and 42°, from 

 Council Bluff, on the east, to Benicia, in Cali- 

 fornia, illustrates this feature, although an 

 exaggerated representation of the slopes, — the 

 height being seventy times too great for the 

 length. 



In the Andes the eastern slope is about 60 

 feet in a mile, and the western 100 to 150 feet ; 

 the passes are at heights from 12,500 to 16,160 

 feet, and the highest peak — Sorata in Bolivia — 

 25,290 feet. The slope is much more rapid 

 than in the Rocky Mountains. But there is 

 the same kind of mountain-mass variously 

 diversified with ridges and plateaus. The ex- 

 istence of the great mountain-mass and its 

 plateaus is directly connected with the exist- 

 ence of the main ridges. But it will be shown 

 in another place that the ridges may have 

 existed long before the mass had its present 

 elevation above the sea. 



In the Appalachians — which include all the 

 mountains from Georgia to the Gulf of St. 

 Lawrence — the mountain-mass is very much 

 smaller and the component ridges are rela- 

 tively more distinct and numerous, and still 

 the general features are on the same principle. 

 The greatest heights — those of North Carolina 

 — are between 6000 and 6800 feet. 



The Rocky Mountains, Andes, and Appa- 

 lachians represent the three types of chains : 

 (1) the broad and lofty plateau type ; (2) the 

 narrow and lofty ridgy type, of which the 

 Himalayas are another example ; (3) the broad 

 and many-folded type, of which the Juras are 

 another example. 



Illustrations. — It is common to err in estimating 

 the angle of a slope. To the eyes of most travellers, a 



3 



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