64 IMPROVED FISHERY HARBOUR ACCOMMODATION 



Alderney, the Roost of Sumburgh, the term roost being 

 the Orkney and Shetland appellation. 



These, according to the currents of tides, last a certain 

 length of time, and are greatly exaggerated, or partially 

 eased, by coinciding or opposing winds. Their position 

 also sometimes varies with the wind, as at Portland, the 

 race being nearer or more distant from the shore as the 

 wind is off or on the land. 



These races become, in fact, breakwaters to the neigh- 

 bouring shore during the continuance of the current, but as 

 they diminish the rough water being no longer broken, 

 comes quite home on the coast. 



At Portland this is particularly evident, and seamen 

 constantly run inside the race, close to the Bill, and thus 

 avoid the race, when they have a commanding breeze, or 

 with a steamer. These disturbances are due to the 

 rapidity of the current running Over an uneven bottom, 

 whether it be sand or rock. At Portland, for instance, the 

 bottom, in the form of a ledge, rises suddenly from depths 

 of 12 to 40 fathoms to those of 5 and 10 fathoms, and the 

 currents meeting with this opposition, the water ascends 

 from one side of the obstruction, and, falling down the 

 other, collides with the bottom, and in its recoil therefrom 

 causes the irregular and broken sea in question. This 

 raging of the sea is greatly aggravated by an opposing 

 swell to the course of the current ; and at page 5 3 of his 

 work, Mr. Stevenson says : " From careful inquiries, as 

 well as from actual personal experience of such dangerous 

 breaking waters as the Bore of Duncansby, and the Merry 

 Men of May in the Pentland Firth, and several others, it 

 appears that the true cause is. the swell of the ocean en- 

 countering an opposing tidal current'' 



As to those particular instances the writer cannot speak 



