AND OTHER WATER WAVES 211 



In this connection the position of the Skerries 

 Bank, north-east of Start Point, should be com- 

 pared with that of the Shambles. Portland Bill 

 terminates, on the eastern side, the largest bay 

 on our south coast. Start Point similarly termi- 

 nates the second largest bay. On the up-channel 

 side of each is a sand-bank, which, from its situa- 

 tion, and from the absence of a corresponding bank 

 on the west of the promontory, suggests rather 

 the continuous current of a river than the alter- 

 nating currents of the tides. Of all the causes 

 which produce this curious arrangement the rela- 

 tion of the time of turn of the tidal stream to 

 the turn of the tidal level is, perhaps, the most 

 important and the most likely to escape notice. 



The accompanying diagrams show the relation 

 between the times of the vertical and horizontal 

 oscillations of the tide at Portland Bill. 



The Formation of Patches of Shingle upon a Sandy 

 Beach by the Action of Breakers 



The surface of the beach at Branksome Chine 

 is usually pure sand, but many stones derived from 

 the wasting of the gravelly cliffs are buried beneath 

 it. Under certain conditions the wash of the 

 breakers begins to convert the sandy to a shingly 



