ALONG SHORE 



137 



water. For a different set of forces regulates 

 the form and motion of the crest in mid-ocean. 

 The white-cap on the open sea is lifted to a 

 height where it cannot sustain itself by the push 

 up of the water and the wind ; but the wave has 

 no beach beneath it to concentrate strength 

 in the cap. Driving upon the coast, the cap is 

 flung forward by the wedging process already 

 described, and, if there is a fierce storm, it 

 is often shot up the shore to a great height. 

 Light-houses on rocky ledges far above the sea- 

 level have been frequently washed over and 

 destroyed by these enormous breakers, and 

 upon the cliffs of the Irish coast the waves 

 sometimes rush up fully two hundred feet. 

 The blow struck upon the cliffs by such masses 

 of water is estimated at from two to three tons 

 to the square foot ; and a mile back from the 

 shore the ground can be felt to tremble under 

 the terrific impact. It is the sharp, upward 

 incline of the shore bottom that makes such 

 waves possible. On the open sea they could 

 not by any chance rise to such a height. The 

 maximum of the Atlantic wave has already 

 been given at forty-three feet, and not even in 

 the Bearing Forties, in the most violent storm 

 ever known to roaring sea-captains, has a 



Thepow* 

 of the 

 waves. 



