338 WAVES OF SAND AND SNOW 



speed of the current required to produce waves 

 1248 inches long would be 324 feet per second 

 instead of 2* 93 feet per second. 



The longest waves which I have measured were 

 on the North Goodwins, which had a length of 

 847 inches. 



Sand-waves 124-8 inches long in the Dovey 

 Estuary were formed by a current of 2- 93 feet 

 per second. If the length be proportional to the 

 square of the speed of current, then the sand- 

 waves on the North Goodwins would require for 

 their formation a current of 7*6 feet per second, or 

 452 knots, which is somewhere about the strength 

 which would be met with at spring tides in such a 

 situation. 



The group of steepest sand-waves measured on 

 a dried-out sandbank had lengths almost exactly 

 fourteen times as great as their height. If the 

 longest sand -waves measured on the Goodwins have 

 at their full development the same shape, their 

 height would be 5 feet. I do not know if heights 

 as large as this have been recorded. The Ri^v. 

 John Gilmore, in a book called " Storm Warriors," 

 relating to lifeboat work on the Goodwin Sands, 

 speaks of the lifeboat continually grounding on 

 " ridges 2 or 3 feet high." 



The sand-reefs of the Mississippi are not groups 



