RELIEF FEATURES 11 



sea-level, as because of its distinct rise above the plain along one 

 side of it. The Piedmont Plateau, which lies between the Appala- 

 chian Mountains and the Atlantic Coastal Plain of the United States, 

 is not very high, but it is enough higher than the Coastal Plain to be 

 distinctly set off from it. A large part of this plateau is, however, 

 not so high as much of the great interior plain of the continent. 



Some plateaus lie between mountains on the one hand and plains 

 on the other, as in the case of the Piedmont Plateau. Others lie 

 between mountains, as the plateaus of central Asia (Fig. 6), Mexico, 

 and the western part of the United States (Fig. 7) . Such plateaus 

 do not appear higher than their surroundings. Other plateaus rise 

 directly from the sea, as Greenland and parts of Africa. The total 

 area of plateaus is great, though less than that of plains. 



Habitability. Except in low latitudes, high plateaus are too 

 cold to be well adapted to agriculture, and their rainfall is often 

 scanty. High plateaus are therefore less well fitted for human habi- 

 tation than plains, and are usually sparsely settled. Low plateaus, 

 on the other hand, may have a climate as favorable as that of plains. 

 In low latitudes, even high plateaus may have a hospitable climate. 

 The plateau of Mexico is an example. 



Origin. Plateaus attained their height in various ways. In 

 some cases their surroundings probably sank away from them leav- 

 ing them relatively high; in others, plateaus may have been elevated 

 above their surroundings; while in still others, they have been built 

 up by floods of lava. Such is the lava plateau of the northwestern 

 part of the United States (Fig. 8). 



Mountains 



Mountains are conspicuously high lands which have but slight 

 summit areas. The tops of the loftiest mountains are between five 

 and six miles above the sea, but most mountains have not half 

 this height. The highest mountains tower above any plateaus, but 

 many mountains are lower than the highest plateaus. Few moun- 

 tains reach the height of the Plateau of Tibet, 15,000 to 16,000 feet. 



Mountains are unlike plateaus of similar elevation in having 

 little stretch of surface at the top. In the case of mountain peaks, 

 this is shown by the name. A mountain ridge or range may be long, 



