CHAPTER XXII 



THE SURFACE OF THE EARTH 



Everybody has observed that the surface of the 

 earth is not smooth, but more or less irregular. Some 

 of these irregularities, as mountains and large valleys, 

 are very conspicuous, while others, as hills, ravines, 

 ridges, cliffs, and flats, are less conspicuous, but more 

 widely distributed. These irregularities, which make 

 up the relief features of the earth, may be classified as 

 follows : continents and oceans ; mountains, plateaus, 

 and plains; and minor land forms. 



Continents and oceans. The relief features of the 

 first group, the continents and ocean basins, have prac- 

 tically always occupied the positions they now have. 

 It is not positively known how they came to originate 

 or to occupy these positions. When the earth cooled 

 from its original heated condition, there was a down 

 folding where the ocean beds now are, and a corres- 

 ponding elevation over the continental areas. When 

 the surface of the earth was cool enough to allow the 

 atmospheric waters to remain, they accumulated in 

 the depressions, and thus made the seas. 



Although in name there are five great oceans, in 

 reality there is but one. As all the ocean water of the 



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