196 Proceedings of the Royal Irish Academy. 



irreconcilable with the halting of the same ice-sheet at Draperstown at but a 

 small elevation above the sea, unless it be supposed that a banier existed here 

 in the shape of a great mass of local ice. Against the obvious objection that 

 suggests itself, that the earlier Scottish drifts may have been cleaned out by 

 the later ice advancing from the south-west, it may be remarked that had this 

 taken place, some evidence should be forthcoming of the iucorpoi-ation of these 

 eastern erratics in the newer drifts, to form a composite boulder-clay, as is 

 invariably the case in Inishowen, where, as we liave aheady seen, such a 

 succession of events actually took place. Moreover, the sites of these sections 

 are very similar to those in the country south of Lough Foyle, where the 

 earlier drift has been preserved intact as a pure and unmixed eastern boulder- 

 clay. Thus it would seem that to the east of Drapei-stown the local and the 

 invading ice sheets were actually in contact,. the former beiug chiefly ice 

 centring in the Sperrin Mountains, though reinforced possibly by ice from 

 the west. 



VI. — The Donegal Glaciation dtjrisg its Maximum Puask. 



While the Scottish ice was gradually encroaching on the eastern parts of 

 the region, and slowly thrusting its ice-front towards the west, a series of 

 glaciers, centring in the Highlands of Donegal, was growing outwards and 

 creeping in the diiection of the invader. Of this early phase no trace now 

 exists. The great erosive action of the prolonged ice-movement that followed 

 has swept away all its products and completely effaced all the effects of its 

 glaciation, save one — the corries. 



If the early stages of the glaciation of Donegal are wrapped in obscurity, 

 the story of the ice at its maximum phase is, on the other hand, in its broad 

 outlines by no means difficult to decipher, for the approximate direction 

 followed by the lower and even upper currents of the great ice-sheet can be 

 very readily ascertained. The striae are of sufficient abundance to prove a 

 general divergence of the ice from the central portion of the mountainous 

 district. The erratics furnish confirmation of this outward flow, the boidder 

 streams participating in the dominant movement and passing ladiaUy down 

 the larger depressions towards the peripheral belt of deposition. 



The piincipal Line of ice-shedding shown on the geneiul map (PI. IX) was 

 in the main coincident with part of the present piincipal watershed of Donegal. 

 It ran roughly from Clogher Xorth, in the north-west, passed Croveenananta, 

 Lavagh More, Blue Stack, to the south of Binmore, Croaghbames, 

 Croaghaniwore, Croaghconnellagh, to Bamesmore in the south-east. 

 This great rounded Don^al ice-shed continued to the south-east of the 

 high granite hiUs of Bamesmore, along the moimtains to Lough Dei-g. On 



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