208 WAVES OF THE SEA 



maintained by this and other detritus settling from 

 suspension in the repeated horizontal circulation 

 of water eddying round a vertical axis on the east 

 side of Portland. 



The course of the currents is as follows : ' The 

 outset from the West Bay from 2 hours to 1 1 hours 

 on the days of full and new moon, having assumed 

 its eastern course, rushes with great violence over 

 Portland Ledge. High water at the Bill occurs at 

 about 5^ hours F:. and C. (i.e., on the days of 

 full and new moon). At 6 hours 20 minutes this 

 stream is met at right angles a short distance east 

 of the ledge by a strong stream from East Portland 

 Bay. This stream lasts for 9^ hours. " These 

 united streams press on towards the Shambles, 

 which they cross about east by north, running 

 3f knots." 



The bank, which is composed of coarse ,sand 

 and gravel, rises suddenly on the south from the 

 depth of 10 fathoms. The approach on the north 

 is more gradual. The streams run across the shoal 

 at 3 to 4 knots during spring tides, and waves 

 break heavily upon it. The surface is strongly 

 rippled, and the ridges are in motion even in 

 fine weather. The shoal does not persist, there- 



1 See " The Pilot's Handbook for the English Channel," by 

 Commander J. W. King, R.N., twelfth edition, 1893. 



