Chari,E8W0UTH — Glacial Geologjj of North-West of Ireland. 305 



The ice caused the removal of the loose debris which had accmniilated in 

 pre-glaeial times as talus slopes at the foot of the inland cliffs, and of the 

 local sub-soil formed by the disintegration of rock in situ. This material, 

 carried on to the peripheral plains, choked the valleys and served as a mask, 

 obscuring and obliterating the inequalities in the surface. This suggests 

 that prior to the period of glaciation the dependence of the contour of the 

 country on its geological structure was closer than at present, and its relief 

 considerably more pronounced. Yet in many areas, where rocks of varying 

 resistance crop out, glacial action has greatly accentuated the differential 

 effect on the physical features, e.g., in the Glenalla and Eathmullan areas. 



It is not my prirpose here to discuss at any length the perennial question, 

 " does ice erode ? " but to state as concisely as may be the impressions 

 formed during this glacial investigation. The valleys of N.-W. Ireland are 

 demonstrably, like those of N.-E. Ireland, post-Eoeene. They cut through the 

 basalt dykes of Derryveagh and the Barnesmore granite of Tertiary age.^ 

 They possess in the Donegal hills hanging tributary valleys, and exhibit 

 typical U-shaped cross-sections. Tiiese the writer regards as rejuvenation 

 features produced anterior to the glacial period and modified only by ice 

 erosion. 



A coastal strip of varying width and of an average altitude of about 200 

 feet, O.D., or rather less, fringes Donegal on the north and west. This plain 

 is well seen in the area of the River Erne below Belleek ; it skirts the eastern 

 shores of Donegal Bay, where it is largely covered with drumlins, and forms all 

 the floor of the amphitheatre in which lies Lough Eske, extending to the foot of 

 the schist hills north of this lake ; it is very well developed over the country 

 north of Ardara, running inland to Glenties and the mouths of the valleys of 

 the Shallogan and Owenea rivers ; to it belongs the whole of the Eosses, where 

 it is bounded on the east by the fall-line passing by Crolly ; it extends bay- 

 like up the Gweebarra depression and includes the flat country stretching 

 inland from the northern coast almost to the foot of the Derryreel Eidge, and 

 from Sheephaven almost as far as Gleuveagh. 



This plain is not due to differential weathering ; it cuts across all 

 boundaries, and affects Carboniferous rocks, schist and granite; the two 

 strongly-contrasted types of scenery of the Donegal granite country, the 

 mountainous Derryveagh on the one hand, and the low reliefless Eosses on 

 the other, cannot be explained by this process. 



This country is a peneplain into which, as the result of late-Tertiary uplift, 



' Compare tlie argument of Sir A. Geikie (Ancient Volcanoes of Great Britain, vol. ii, 

 ■p. 459). 



