204 WAVES OF THE SEA 



ally increasing in strength as it approaches the 

 Bill, where it has acquired such velocity as to 

 extend far beyond that point before it turns to 

 the east. This tide out of the west bay acquires 

 its greatest velocity when the tidal stream in this 

 part of the English Channel is running to the east- 

 ward. While, therefore, the large shingle is driven 

 to the focus of the waves at Chesilton, the smallest 

 shingle, the sand, and chips are presumably re- 

 moved by the undertow. What becomes of some 

 of the material so removed is suggested in the 

 section relating to the Shambles Shoal. 



Marked gradation in size of shingle is a charac- 

 teristic of beaches sheltered at one end by a 

 natural or artificial groyne. I have not heard of 

 conspicuous cases of such gradation on long 

 beaches with a nearly uniform exposure such, 

 e.g., as that at Aldeburgh in Suffolk. This being so, 

 my explanation of the grading as due to one-sided 

 shelter would probably have found readier accept- 

 ance but for the attractions of a previous sugges- 

 tion by Sir John Coode. He noticed that a large 

 pebble isolated on a surface of small shingle was 

 rolled about by the wash of the waves even when 

 this travelled over the interlocked smaller pebbles 

 without disturbing them. He said that large stones 

 would travel quickly along the Chesil Beach from 



