200 WAVES OF SAND AND SNOW 



which recall by their position relatively to a head- 

 land, and also by their shape, the banner cloud of 

 mountain districts, the difference being that the 

 sandbank is produced in the eddy formed by a 

 horizontal projection, the banner cloud in that due 

 to an upward projection. The Shambles Shoal, 

 near Portland Bill, is an excellent example of a 

 shoal analogous to the banner cloud. It is on the 

 east side of the promontory, which is the lee when 

 the current of the flood tide is running. There is 

 no corresponding shoal on the west side. The 

 same arrangement is found near Start Point, in 

 Devonshire, viz., a shoal on the east, but none 

 on the west. I have offered as an explanation 

 that when the current flows up-channel — i.e., east- 

 wards — it is for most of the time above mean sea- 

 level and carries much sand from the beaches with 

 which the water is then in contact and which are 

 then stirred up by waves. During most of the 

 time when the current ebbs westwards, down- 

 channel, the water is below mean sea-level, it is 

 not in contact with the thick and steep part 

 of the beach, and the waves beat less strongly 

 upon the flatter part which is submerged.' 

 Thus, as far as the formation of sandbanks is 



^ See "Waves of the Sea and other Water Waves," by 

 Vaughan Cornish, Part II, p. 206. 



