19i Proceedings of the Royal Irish Academy. 



This line, as a glance at the map shows, possesses two great salients, to 

 the north and south i-espectively of the Speniu Mountains. Tliey are in 

 part to be attributed to the barrier of local ice centring in these hills, which 

 probably deflected the invading ice to the north-west and south-west, iu part 

 to the directions of principal thrust of the Scottish ice. This was split off the 

 north-east coast of Antrim into two great streams, the one proceeding, as 

 Dr. A. E. Dwerryhouse has shown, iu an approximately east-west direction, 

 as on Eathlin Island and Fair Head, the other rouglily soulh-west aud south 

 over the counties of Antiini and Down. This ice, after surmountiug the 

 Antrim plateau, would find to the south-west iu the direction of Lough Neagh 

 and Monaghan no hilly barrier t^ its progress. Obstructed by the Sperrin 

 Mountains and their glaciers, it would therefore fiud relief by pressing down 

 towards the Glogher valley and by fanning over the Monaghan region. 



Mr. W. B. Wright ' has clearly i-ecognized the comparatively restricted 

 area covered by the Scottish ice in Iv^orth Ireland : indeed his map (fig. 27) 

 depicting the directions of ice-flow in Britain errs rather on the side of 

 representing that area as somewhat smaller than it actually was — an error 

 doubtless due to the conflicting e\^deuee of the later glaciation. Of other 

 writers, Mr. T. Hallissy alone has expressed views as to the western limit of 

 the Scottish ice which are at all in agreement with the results obtaiued in 

 this investigation. In his paper on the Geology of Clare Island he writes - 

 with reference to this question : — " Judging from the distribution of these 

 foreign boulders, it seems likely that a line rimniug south-east from the 

 mouth of the river Foyle marks approximately the limit to which the Scottish 

 glacier penetrated into the country " — though in the same year (1914), in the 

 Memoir of the Geological Survey descriptive of the Monaghan area, he 

 doubtfully attributes the K.K-S.W. drift ridges of that district to this same 

 Scottish ice (p. 16). 



The relationship of this invading ice to the Donegal glaciers is very 

 obscure. In the south, no evidence was obtained on this point. 



In the north, evidence of a kind is not lacking. A crucial section would 

 appear to be that of Low Moor Eoad quai-ry in ihe city of Londonderry, to 

 wliich reference has already been made, and wliieh has been fully described 

 in the Londonderry Memoir (p. 38) from which the following has been 

 taken: — 



" A fine section of gravel and sand, resting on solid rock, with Jat«r 

 boulder-clay covering it, is laid open to view. In the bottom of the pit 

 over fifty feet of reddish sharp sand, with coarse and fine iiaegularly 



- Quatemary Ice Age (191-t), fig. 27. 



' Proc Roy. Irish Academy, vol. xsxi (1914), Pt. 7, p. 9. 



