40 THE WORLD'S LUMBER ROOM. 



So much for the work done by wind-driven sand. We 

 shall see presently that it is no less effectual when urged by 

 water. 



The waves of the sea, indeed, as they thunder against the 

 cliffs, are powerful enough to do a large amount of rough 

 work without assistance j but what tremendous blows they 

 must deal when they rush up to a height of perhaps a 

 hundred feet, laden, as of course they often are, not only 

 with sand and pebbles, but even with large stones. 



When especially furious, they will tear down piers and 

 jetties and carry away long lengths of sea-wall, and at all 

 times they are more or less busy undermining the cliffs, and 

 when these at last fall in by their own weight, the 'fragments 

 are dashed one against the other, broken into smaller frag- 

 ments, rolled and rounded into pebbles and ground into 

 sand, and perhaps swept farther along the coast and cast up 

 as beds of sand, gravel, or shingle. 



With all their fuss and fury, however, the waves are 

 usually unable to keep pace with the silent workers above 

 frost, thaw, atmosphere, &c. And, accordingly, though 

 the cliffs are hollowed into caverns here and there, they do 

 not on the whole overhang the sea, but slope away from it, 

 showing that the wear and tear proceed after all at a more 

 rapid rate above than below. 



Perhaps the largest shingle-bed in the world is that which 

 lies on the east coast of Patagonia, and is between six and 

 seven hundred miles in length. Its average width is two 

 hundred miles, and its average thickness fifty feet, which, in 

 at least one place, is increased to more than two hundred 

 feet ; and if the pebbles alone, without the accompanying 



