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 Roaring Forties, in the most violent storm 
ever known to roaring sea-captains, has a 
The power 
of the 
waves. 
