GENERAL FEATURES OF THE EARTH. 



17 



miles, and the fall on the other side for 400 to 500 miles ; the 

 at the summit have a height of 4,944 to 10,000 feet; and above 



passes 

 them, 



Fig. 2. 



as well as over different parts of the slopes (espe- 

 cially on the west), there are ridges carrying the 

 altitude above 14,000 feet. The highest part of 

 the range is in Colorado, where the passes are 

 11,000 to 13,000 feet high; while in latitude 32° 

 the passes are about 5,200 feet. The mountain- 

 mass, therefore, is not a narrow barrier between 

 the east and west, as might be inferred from the 

 ordinary maps, but a vast yet gentle swell of the 

 surface, having a base 1,000 miles in breadth, and 

 the slopes diversified with various mountain -ridges, 

 or spreading out in plateaus at different levels. 



The annexed section (Fig. 2) of the Rocky i'|||J ro 

 Mountains along the parallels 41° and 42°, from »3 ftS-E. 

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

 nia, illustrates this feature, although an exagger- 

 ated 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 existence of the great 

 mountain-mass and its plateaus is directly con- 

 nected with the existence 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. Law- 

 rence — the mountain-mass is very much smaller, 

 and the component ridges are relatively more dis- 

 tinct and numerous; and still the general features 

 are on the same principle. The greatest heights 

 — those of North Carolina — are between 6,000 

 and 6.707 feet, and the average height is about 

 3,000 feet. 



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The Rocky Mountains, Andes, and Appalachians represent the three 

 2 



