AND OTHER WATER WAVES 193 



think that the reduction in the size of pebbles is 

 accomplished mainly by fracture. Although the 

 principal pebble has its fractured surface rapidly 

 smoothed and rounded, the sharpness of the chips 

 tells the true tale. It is the same with wind-borne 

 sands the larger grains are the best rounded. If 

 comminution really proceeded mainly by rubbing 

 down, it would be the smaller particles which would 

 be the best rounded. 



I was fortunately able to observe on the Chesil 

 Beach, in July, 1897, a part of the wave action by 

 which the sorting of shingle is accomplished. I 

 was on the beach opposite Chickerell when there 

 was a light easterly wind, and the small breakers 

 made by it were depleting the steep face of the 

 beach. A glance at the map shows that wind from 

 the east has a small length of fetch, and that the 

 waves it makes cannot be very large anywhere 

 on the beach, and, near Chesilton, must always be 

 very small. The tide was falling at the time of 

 my observation, and the shingle in the band of 

 wet stones exposed above the waves was coarser 

 than that out of their reach. It was evident that 

 the backwash was removing the smaller pebbles 

 and drifting them westwards, leaving the larger in 

 their place. 



The secret of the gradation of shingle upon 

 beaches sheltered at one end from large waves 



