CH. XI.] THE SEA AND ITS WORK. 167 



the waves. Rain, frost, and other atmospheric agents, 

 playing their part in the work of destruction, attack the clift 

 and dislodge masses of rock which come tumbling down to 

 its base, where they accumulate as a line of rubbish. As 

 soon as the fragments are brought within reach of the waves, 

 they are rolled against the cliff, bruising and battering the 

 face of the rock, while the fragments themselves are apt to 

 get shivered in the fray. 



During violent gales the breakers acquire unusual power, 

 and are able to move rocks of enormous weight. On the 

 western coast of Britain, where the Atlantic breakers roll in 

 upon the shore, they have been known to exert a pressure 

 of between three and four tons on every square foot of 

 surface exposed to their fury. Even in summer, these waves 

 break upon the coast with a pressure of about 600 pounds 

 per square foot; and, in winter, this force is often trebled. 

 It is easy to believe that such masses of moving water can 

 carry with them huge blocks of stone, and hurling these 

 against the shore, can breach it just as effectually as though 

 it were attacked by the blows of a battering-ram. In fact, 

 whether in storm or in calm, a cannonade, more or less 

 sharp, is constantly kept up against the coast, the ammuni- 

 tion being supplied by the ruins of the coast itself. 



Were the waves to break upon the shore without the aid 

 of any fragments of rock, the mere weight of water would 

 naturally effect some amount of destruction; but, there is 

 reason to believe that, in most cases, this would be 

 comparatively slight. It has been already shown that a 

 river erodes its channel, not so much by its own friction, as 

 by that of the sedimentary matter which it sweeps along in 

 its course. In like manner, the wear and tear of the waves 

 themselves is insignificant compared with that wrought by 

 the boulders and pebbles, the gravel and sand, which they 



