INSTABILITY OF SAND-BEACHES 



67 



materials are apt to be in a state of continued instability; 

 their sands are generally moving- with considerable speed in 

 the direction in which they are borne by the shore currents. 

 The march of the sands along the shore continues until they 



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Moderate Surges seen along their Crests 



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The shore is in its nature alluvial, and the most approved method of protection by means of sea-wall, 

 together with spur breakwaters, is shown. The object of these breakwaters is to keep the sand and 

 pebbles from working along the beach under the influence of the waves and currents. 



have attained the extremity of the coast, or found their far- 

 ther progress obstructed by some strong ocean current which 

 sweeps the incoherent matter away into the depths. Thus 

 along the Atlantic shore from Cape Hatteras to Cape Florida 



