FOR GREAT BRITAIN AND IRELAND. 101 



construction of the breakwaters at Holyhead and Port- 

 land. The improvement consists in depositing the rough 

 materials from stagings of timber, elevated a considerable 

 height above high water. The stones are brought on the 

 staging in waggons, through the bottoms of which they are 

 discharged into the sea. The principle on which these 

 stagings are designed, is that of offering the smallest 

 possible resistance to the sea, the under structure consist- 

 ing of nothing else than single upright piles for supporting 

 each roadway. 



The great success which has attended this method is 

 well known, but for the majority of fishing-boat harbours, 

 this method requires too much material ; for large refuge 

 harbours however, which may be a development of fish- 

 ing harbours already existing, it is quite possible this 

 method may be again employed, as at Portland and Holy- 

 head. 



Two great points to recommend this mode are first, the 

 rapidity of construction, and secondly, the opportunity of 

 employing a large amount of unskilled labour ; thirdly, 

 refuse stone may be used, as in the case of Portland, where 

 the cap stone, covering the beds of good Portland stone, 

 was used, and cost only the labour of removal. As is 

 well known, the labour was that of convicts, under 

 qualified leading men. 



MISCELLANEOUS SUBJECTS IN CONNECTION WITH 

 HARBOURS. 



DEPOSIT OF SILT, SAND, &c. 



Decrease in depth has been caused in some harbours 

 by deposit of mud, sand, or gravel. This is a great evil, 

 and very difficult to cure. 



