BEACH CUSPS 



241 



which are completely buried in Fig. 3, and the bays between. 

 We also note that each break in the seaweed exactly marks a 

 bayhead. The gravel cusps below are still beneath the water. 

 On one occasion 1 saw a continuous wall of seaweed flunc 

 upon the beach, saw the water ponded behind it until finally 

 weaker points in the wall yielded to the pressure and broke, and 

 openings were established that guided the outflow of all sub- 

 sequent great waves. It seems to be clear that the bays between 



FlG. 3. — Moment of wave retreat. 



the stony promontories are scoured out by water escaping from 

 behind the barrier above. That weak points should occur is 

 inevitable. It is not conceivable that the waves could cast up a 

 line of weed so perfectly homogeneous as to present the same 

 resistance to outflowing water all along the line. Once a current 

 is established across the crest, its lightness causes the weed to 

 float away in the stream until the pebbles below are bared, and 

 then washed down the beach in the narrow rushing stream. 

 The weed where unbroken protects the stony ridge as the paper 

 pattern protects glass from the sand-blast. Furthermore it con- 

 centrates the water on the unprotected spots. It may be thought 



