830 ME. J. E. KILEOE ON DIEECTIONS OF ICE-PLOW 



ocean-bed, probably to the verge of the Atlantic trough, some 90 

 miles distant from the Lewisian chain of islands *. 



It maj' perhaps be questioned whether the Scottish ice-sheet, 

 impinging on the Irish coast, was of sufficient thickness to breast 

 and overtop the Antrim coast-line, when little less precipitous than 

 it now is, and achieve those phenomena with which we accredit it 

 in the Irish area. As bearing upon this interesting point, the 

 foUowing data and considerations are presented, viz. : — 



Striae bearing westiuard have been observedf about the centre of the 

 Nephin Group, Co. Mayo, at the 1100-feet contour. Dr. J. GeiMe 

 states that an ice-sheet, after crossing the Minch from the Scottish 

 Highlands, attained an elevation of not less than 1600 feet in N'orth 

 Harris ±; that in South TJist glaciation is traceable up to about 

 1650 feet or more, on Beinn-Mhor t ; and that " scratches may be 

 traced .... up to an elevation of 3500 feet at least," in the High- 

 lands §. The same author believes that ice buried Scotland to a 

 depth of several thousand feet, only a few hill-tops rising above the 

 general level of the Mer de glace §. And in his ' Scenery of Scot- 

 land,' Dr. Archibald GeiMe records striae at a height of 2250 feet on 

 Ben Lomond |1. 



If we conceive these points connected by an ideal plane, the 

 plane would mark a minimum upward limit of glaciation during the 

 period of intensest cold ; and ascending by an imperceptible gradient 

 towards the Grampians, would be some 2000 feet above the present 

 sea-level at the Antiim coast-line. Allowing for unobserved and 

 effaced glacial traces, at higher elevations than the points referred 

 to, also for the depth of ice and neve necessary to leave appreciable 

 traces on the more elevated surfaces of rock over which the mass 

 moved, the " general level of the Mt'.r de glace,'" mentioned in the 

 above extract, probably attained a much higher level than the plane 

 which indicates the limit of observed glaciation. The ice-sheet 

 probably exceeded 3000 feet in the jSTorth Channel, the present 

 depth of water being 700 ; and urging its way westward, it over- 

 topped the coast escarpment by some thousand feet or more. 



It has hitherto been supposed that the Irish Mer de glace was 

 sufficient to obstruct the Scottish ice-current and divert it north- 

 ward, after its encroachment to some extent upon the territory of 

 the former. But striae have been observed bearing westward, from 

 the entrance to Lough Poyle throughout the county of Donegal to 

 the western sea-board, which could not have resulted otherwise than 

 from ice continuous with and moving en masse with the sheet 

 which blocked up the adjacent oceanic area, as ali-eady described. 

 Such an ice-movement alone satisfactorily accounts for the occurrence 

 of chalk- flints in the drift of Inishowen which bestrews the jS'orthern 

 Donegal coast from Inishowen Head to llalin Head. What thus 

 at this period hindered the northward flow in Donegal would, a 



* See Messrs. Peacb and Home's map above referred to. Dr. Croll supposes 

 the ice-cliff terminating the great ice-sheet westward to have been about 170 

 miles distant, see Chart, p. 449, ' Chmate and Time,' 1875. 



t By myself in 1878. § ' Great Ice Age,' ed. 1 (1874), pp. 83, 86. 



+ Paper sup. cit p. 832. 1| ' Scenery of Scotland,' ed. 2 (1887), p. 252, 



