102 IMPROVED FISHERY HARBOUR ACCOMMODATION 



Where there is too much mud, excavation and hand or 

 steam dredging are employed in the removal. 



In respect of mud, very effective work is constantly per- 

 formed, but both sand and gravel are very difficult to deal 

 with ; in fact, the former would almost seem to have the 

 power of propagating itself, for it is noticed that in many 

 harbours naturally existing, there are banks quite moderate 

 in size from which barges have removed the sand for agri- 

 cultural and other purposes, from time immemorial, which 

 banks suffer no perceptible decrease. In the case of small 

 banks where this is the case, it is clear an annual deposit 

 must be made. 



In the present state of our knowledge it would be little 

 less than quackery, observes Mr. Stevenson, to lay down 

 rules for the guidance of the engineer. 



MOVEMENT OF SHINGLE. 



There is a large accumulation of shingle on many parts of 

 our coast, which may in many cases be traced to the neigh- 

 bouring cliffs, in which very extensive beds of gravel, &c., 

 often exist. Wherever the prevalent winds blow obliquely 

 on the shore, the waves cause the beach to travel more or 

 less along it, and on the south coast of England they partly 

 obstruct the entrances of harbours. 



Where such accumulations take place, it is desirable to 

 place the entrances of harbours in as windward a position 

 as possible, and on the south coast of England to point 

 the entrance to the south-east, and to keep the beach 

 back with piers. In addition to a pair of piers between 

 which the river runs into the sea, a jetty has sometimes 

 been erected west of the west pier to catch the travelling 

 shingle. 



