ACTION OF WAVES ON SEA-CLIFFS 9 



surging violently against its base, but we observe that tliey do 

 not strike an effective blow, but merely swash up and down, 

 as they break against the steep. As we shall shortly see, 

 their action is impotent as compared to what it is when the 

 cliffs do not descend into deep water, but have something 

 like a beach at their base. 



The fact is that the ocean weaves, when they beat against 

 a rock-bound shore where the firm cliffs descend into deep 

 water, have very little destructive power. When they strike 

 the shore they ma}' apply a pressure of from one to three 

 tons per square foot of surface against which they run, but 

 this can only break away the masses of stone which have been 

 loosened by the action of frost or the other processes of 

 decay. On a shore which has recently been overridden by 

 the glacial ice, the weaker kinds of rock have been pretty gen- 

 erally worn away, and it is only slowly that they yield to the 

 sea's assault. Yet, now^ and then masses tumble from the top 

 of the cliff, so that here and there, even on the steepest shores, 

 we find where the debris from the precipices has been suffi- 

 cient to make a beach-like accumulation such as is shown in 

 the illustration (page 10). As soon as this mass of debris 

 comes near enough to the surface to be much affected by the 

 dragging action of the waves as they surge against the steep, 

 the stones are arranged by the waves so that they assume 

 more distinctly the beach form. In this state of the shore the 

 surges are at last able to do their effective work. We may 

 observe them rolling in from the deep in the lorm of broad 

 folds of the ocean's surface ; when the advancing margm of 

 each wave arrives at the shallower water at the outer part 

 of the inclined plane of debris, the friction of the bottom 

 opposes the forward movement, and causes the front of the 



