WAVES AS DESTROYERS AND BUILDERS 159 



prevents the wind from getting sufficient hold upon the 

 water to topple over the crests, and thus the danger of being 

 swamped is averted. It has been found that oil will spread 

 out even in the direction of the severest wind. 



Although sometimes waves are spoken of as " mountain 

 high," it rarely happens that the height from trough to 

 crest is over 50 ft. The movement of the waves stirs up 

 the water and enables it more freely to absorb the air which 

 is so necessary for the existence of water animals. 



FINGAL'S CAVE 



Waves as Destroyers and Builders. Wherever the 

 waves strike on an unprotected shore, they wear it away. 

 The rapidity of the cutting and the forms carved depend upon 

 the strength of the waves and the kind of shore. Wherever 

 there is a point of weakness along the shore, there the waves 

 cut back more rapidly. The harder parts stand out sharply 



