EFFECT OF POCKET-BEACHES ON JJAKJIORS 59 



the sides receive a certain amount of material wliich the 

 current brought with it, Ijut which the retiring water, shpping 

 between the pebbles, cannot take away. In this manner the 

 little bays grow, cutting deeper into the beach at their heads 

 and extending their horns farther out, until these projections 

 come to the point where the inner lines of breakers beat them 

 down. Each of these small divisions of the shore accumula- 

 tions is in effect of itself a small beach, but it is peculiar in 

 the fact that it is the product of the swash and not of the 

 breakers. 



The numerous pocket-beaches of our cliff shores have 

 a very important influence on the history of the harbors, on 

 which man's relation to the sea so immediately depends. 

 Owing to the migration of the sand and pebbles along the 

 shore, the greater part of this debris would soon find its way 

 into the inlets which afford shelter for ships, and would shal- 

 low the anchorage grounds, or entirely efface them, were it 

 not that the material is caught and imprisoned in the pockets 

 and there ground into .mud, which may be carried away by 

 the current to the open sea. Wherever we observe a shore 

 which by its v^'earing produces much detritus, we are sure to 

 find a number of these beach-mills whereon the bits of rock 

 are ground to powder. From them little pebbly waste 

 escapes seaward, as is shown by the fact that, though in all 

 o-eoloo-ical aees the sea has been at work upon vast stretches 

 of shore-line, it is rare, indeed, that we find in the rocks any 

 of the characteristically ovoidal pebbles which have been 

 shaped by the waves. Even to the cursory eye the beach 

 pebbles have distinct peculiarities which separate them from 

 all other similar fragments. They are always spheroids, that 

 is, they closely approach the globular form, while those which 



