CHAPTER VI 



On the actions which determine the 'longshore transport of 

 beach shingle On the causes which give rise to an arrange- 

 ment of pebbles according to their sizes along the Chesil 

 Beach and certain other beaches On the production and 

 maintenance of the Shambles sand-bank near Portland 

 The formation of patches of shingle upon a sandy beach by 

 the action of breakers. 



On the Actions which Determine the 'Longshore 

 Transport of Beach Shingle 



WHEN the sea is smooth, the shingle of our beaches 

 lies undisturbed by the tidal currents. The 'long- 

 shore drift of beach shingle is therefore ultimately 

 due to the wash of the breakers, and in order to 

 judge of the effect of the tidal currents upon 'long- 

 shore drift, we have to consider how the motion 

 of this wash -water is affected by them. Where 

 the shingle beach is on a straight line of coast 

 where the tidal current runs strongly past the shore 

 while a fairly heavy surf is breaking, the appear- 

 ances presented to the spectator on the shore are 

 deceptive. The breakers discharging at right 

 angles to the shore are noisy and conspicuous ; the 



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