192 WAVES OF THE SEA 



bats, yet the observation of the latter shows that 

 with the ordinarily prevailing westerly winds a stone 

 may travel from Bridport Harbour to Chesilton 

 in a time to be reckoned in days, weeks, or months, 

 and not in decades or centuries. When dealing 

 with the arrangement by sizes of worn beach 

 pebbles, we should therefore seek an explanation 

 in the rapid shifting of the material and not 

 in its relatively slow attrition. Thus I found the 

 average weight of a pebble at Chesilton to be 

 12.8 oz., and at Burton Bradstock, 16 miles away, 

 .028 oz.i.e., 457 times smaller. Prestwich ex- 

 plained this difference of size on the supposition 

 that the pebbles travelled from Chesilton towards 

 Burton (and Bridport), and in transit were 

 reduced from the size seen at the former to that 

 seen at the latter place. Apart from the circum- 

 stance that all the known agencies are to make 

 the principal travel in the opposite direction, let 

 us see what his supposition would involve. It is 

 useful to consider it because of its possible mis- 

 application to other causes where it may be less 

 easy to disprove. In the first place, it would mean 

 an extraordinarily short life for a pebble. In the 

 second place, it would involve the presence all 

 along the beach of an enormous proportion of sharp 

 shingle -chips. My own observations lead me to 



