KiNAHAN — Beaitforfs Dyke, Coast of the Mull of Galloway. 29 



some remarkable changes occurred between that year and 1897 in 

 places, the gulch being considerably deepened, while the northern 

 portion has become forked, a deep new branch having been scooped 

 out to the west of the northern portion of the dyke ; as this branch 

 appears in charts 1897 and 1898, and partially in Barton's chart, we 

 may presume his chart was slightly prior to the others. 



To what causes are these deep-sea currents due ? First, it has to 

 be considered : — to what is the genesis of the gulch due ? Elsewhere 

 it has been suggested that the "Beaufort's Dyke," or gulch, has a 

 connexion with a compound fault — a right-hand heave that can be 

 clearly seen in this portion of the channel. This fault is probably 

 a "trough fault," that is, a combination of two or more lines of 

 breakage and shiftings ; these either formed an open shrinkage fissure, 

 or left the materials in the " trough fault," so broken up, that they 

 were easily lifted and carried away by the ice at the time wlien the 

 great glacier occupied the valley of the basin of the present Irish Sea. 

 One or other, or both, of these forces, combined with the broken-up 

 " fault rock," seems to have been the origin of the gulch. Since 

 then, we know from the sounding in the charts (1867, 1879, 1885, 

 1890, 1894, 1897, and 1898) that the sands, gravels, etc., in this 

 chasm have been continually shifting, which movements must be due 

 to the tidal-waves in combination with wind-waves. 



Haughton, from his investigation of the Tides between Great 

 Britain and Ireland, has proved that the "Head of the tide surface," 

 in the channel, is in the neighbourhood of the Isle of Man.^ He defines 

 the " Head of a tide," a place where the waters are "clumped" up, 

 rising to the greatest height, but having no cui'rents. To the south- 

 ward and northward of the "Head of the tide," in the Irish Sea, 

 there are the " Hinge lines," or the places where there is the least 

 rise of tide and the greatest currents. My experience and inves- 

 tigations have been principally in connexion with the sea to the 

 southward of the "Head of the tide"; but, at the same time, it 

 seems evident that the moving sands, and their adjuncts, of the 

 " Beaufort's Dyke," off the Mull of Galloway, must, more or less, have 

 a connexion with the northern Hinge-line, where there is the least 

 rise of tide and the greatest current. This, however, is a subject 

 that should be worked out by the adventurers who propose the for- 

 mation of a tunnel from Ireland to Scotland. 



^ No perceptible tidal currents occur in a line from Dundrum Bay to Dalby, 

 Isle of Man, and from Douglas, eastward, to Duddon. 



