142 



NATURE FOR ITS OWN SAKE 



Cliff under- 

 mining. 



along, one over another, prove very effective 

 weapons of destruction. They are swept in 

 and out of pools and crevices, lodged in pot- 

 boles, caverns, and scoops, and churned round 

 and round by eddies and currents with a scrape 

 and a grate at every turn. The cliff is thus 

 gradually undermined, and needs only the 

 heave of frost to topple it into the sea. It is 

 protected in a way by its own ruins the outer 

 guard of fallen rock that breaks the force of the 

 waves and besides this, the cliff bases, as well 

 as the fallen bowlders, are sheathed with fringes 

 of seaweed and barnacles ; but still this grind 

 of the surge and the ceaseless beat of the surf 

 finally wear all of them away, and their parti- 

 cles, like the sands from the beaches, are carried 

 out to sea by the under-currents and deposited 

 on the shoals. The diagonal thrust of the 

 waves has something of the effect upon the 

 shore that the running stream has upon its 

 banks. It not only has cutting and wearing 

 power, but it makes currents which carry off 

 what is cut away. 



The greatest wear of the waves is, naturally, 

 where the rock is the softest. A hard quality 

 of rock so hard that it has endured usually 

 appears as the armored prow of every project- 



