THE CONSTITUENTS OF A SEABEACH 6i 



the sea are contioually stirring up and assorting the 

 constituents of the beach in this way. Usually the 

 largest pebbles are thrown up farthest by the advancing 

 waves, and dropped soonest by the backward suck of the 

 retreating water, so that one generally finds a pre- 

 dominance of big pebbles at the top of the beach. But 

 on the flat shore of firm ripple-marked sand lying lower 

 down than the sloping " beach " and only exposed at 

 quite " low tide," one often finds very big pebbles of eight 

 or nine pounds weight scattered here and there and little 

 rubbed or rounded. They have gradually moved down 

 the sloping beach and are too heavy to be thrown back 

 again by the waves of the shallow sea which flows over 

 the flat shores characteristic of much of our south-eastern 

 and southern coast. On some parts of the coast huge 

 banks, consisting exclusively of enormous pebbles as big 

 as a quartern loaf, are piled up by the waves, forming a 

 great ridge often miles in length, as at the celebrated 

 Chesil pebble bank near Weymouth, and at Westward 

 Ho 1 in North Devon. The presence of these specially 

 large pebbles is due to the special character of the rocks 

 which are broken up by the sea to form them, and to the 

 specially powerful wave - compelling winds and tidal 

 currents at the parts of the coast where they are pro- 

 duced. 



One generally finds a selected accumulation of 

 moderate-sized pebbles lower down the beach as the 

 tide recedes, and then still lower down patches of sand 

 alternating with patches or tracts of quite small pebbles 

 not much bigger than a dried pea. They are always 

 assorted in sizes, but the extent of each tract of a given 

 size of pebble varies greatly on different beaches along 

 the coast, and even from day to day on the same shore. 

 The greater or less violence of the wave&, and of the 



