The land may gain temporarily over the sea 

 when sand dunes formed above the high-tide 

 line are held in place by dune plants, 

 such as these in Loch Inchard, Scotland. 



Caves like this one on the Cornish coast of 

 England are hollowed out of soft cliff faces 

 by continuous pounding of the waves. 



tion. The waves, then, appear to be the chief force that wears away 

 and builds up our beaches. Off Dungeness, divers have studied the 

 underwater movement of shingle by an even newer method, one 

 that makes sand fluorescent under ultraviolet light. So the amount 

 of sand or shingle moved along the coast in a given time and under 

 given conditions can be measured. Now that we have seen the 

 destructive forces of the waves, let us turn to their constructive 

 forces, and to the endless variety of the edge of the sea. 



In some areas the land is gaining at the expense of the sea as 

 constructive waves add to the material making up a beach, but the 

 gain may be only a temporary one. Unlike the short and steep 

 destructive storm waves, constructive waves are long and flat. 

 They build up the beach by moving material onto the shore from 

 both inside and outside their break point. In some areas, such as 

 southern California, where the weather pattern is fairly regular, 

 the beaches always build up at the shore line in summer when the 

 waves tend to be low. But in winter, when storms lash the coast, 

 the beaches are eaten away at the top, although the material is 

 deposited just offshore where the water is fifteen to twenty feet deep. 



Beaches, built by the waves, show a multitude of variety, depend- 

 ing on the character of the waves washing up on them, the tide, 

 the nature of their material, and their exposure. Anyone who knows 

 the beaches at Blackpool in England, or Le Touquet in northern 

 France, would notice that the beach profile is not smooth, as are 

 those of Devon, Cornwall, and South Wales. Beaches Hke the one 

 at Blackpool have ridges that can become traps for the unwary as 

 the rising tide floods into the runnel and cuts off' escape. Similar 

 ridges on the beaches of Normandy caused trouble during the 

 invasion landings of World War II. They occur on coasts where 

 the tidal range is fairly large, where the exposure is not too great, 

 and where there is much sand. They may be built up by construc- 

 tive waves, in front of their break point, where there is an over- 

 abundance of sand. Although the ridges tend to be flattened by 

 storm waves, they soon build up again when the low waves return. 

 The beaches exposed to the long Atlantic swells - along Cornwall 

 and the west coasts of Ireland and the Cherbourg Peninsula - have 



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