90 



THE BOTTOM OF THE SEA. 



Straits of Gibraltar have been enlarged by this pro- 

 cess. If, on the other hand, the depth be slight at 

 the base of the cliff, the force of the waves is broken 

 by the opposing rampart of fallen stones, the shore 

 is preserved from destruction, and it is only at some 



Fig. 17 — Waves breaking against a Rock-bound Coast. 



distance from the self-formed talus that the rolled 

 stones are, in the course of ages, carried away by the 

 currents of the ocean. 



The foot of the cliff marks the level of the sea. 

 If this level be changed from any cause, the cliff will 



