AND OTHER WATER WAVES 153 



current, and coarser material begins to be carried 

 backwards ; but this backward movement is more 

 than neutralised by the succeeding forward current, 

 which has the advantage of acting upon material 

 already suspended, or, in the case of large stones, 

 already loosened from their anchorage. 



Next, let us consider the case of waves approach- 

 ing the breaking condition ; and here I can rely 

 upon personal observation, particularly upon the 

 moderately flat, sandy shore between Bournemouth 

 Pier and Branksome Chine, Dorset. When the 

 wave is in this stage the front is much steeper 

 than the back, the upward current (trough to crest) 

 is short -lasting, but very violent. The reversal of 

 horizontal current sets in very suddenly, the shore- 

 ward current attaining its maximum speed very 

 quickly, while the water is heavily charged with 

 the coarser sediment. The change from shore- 

 ward to seaward current and from upward to down- 

 ward current is, on the other hand, very gradual. 

 At its commencement the seaward current is also 

 very gentle, and it only attains great intensity just 

 in time to have its effects upon the coarser sedi- 

 ments reversed by the sudden onset of the shore 

 current which accompanies the advancing wave- 

 crest. 



When the wave actually breaks upon a bare 



