19S Proceedings of iiie Roynl Irish AcaJen 



the investigations of Dr. A. E. Dweriy house and myself, had not been 

 suspected. At a moderate estimate some six to seven thousand square miles 

 of country must have been covered by ice that had its immediate origin in 

 the Denial hills. 



The direction of ice-motion was profoundly affected by the two mountainous 

 masses of Derrj-^'eagh on the north and of Sligo on the south, the fonner, by 

 obstructing the free flow of the ice, being in part responsible for the great 

 extension of the Donegal glaciers to the north-east, and for the oveniding of 

 the Sperrin Mountains ; the latter, for a like reason, for the glaciation of 

 Slieve Beagh and of Monaghan, and also for the great glaciei-s that poured in 

 the extreme north-east down the valley of the Banu, and in the south that 

 fed the " Central Irish Ice." 



The Sligo hills, crowned by a local ice-cap, served as an effective dam to 

 the Donegal ice, causing it to be deflected along their northern face westwards 

 into Donegal Bay, and eastwards and south-eastwards into the northern part 

 of the Central Plain. 



The mass of the Spenin Mountains, with its local radiation, without doubt 

 also barred the progress of the ice in the earlier stages, though later the 

 glaciers piled up along its western flanks, and finally oveirflowed its summits. 

 This obstinacting action of the Spemns would tend to produce a huge ice-sheet 

 of practically level sui-faee, just as on a far lai'ger scale the Jura Moimtains 

 evened up the great Swiss glaciers. 



In the sketch of the glaciation which follows it is proposed, after con- 

 sidering the effects of the ice in the country situated along the ice-shed, t-o 

 give the salient features of the glaciation in the different areas, beginning 

 with the south-west, and working round in a clock-wise direction to the 

 south-east. The order of treatment wiU therefore be the following : — 



1. Country along the Ice-shed. 



2. Drumlin Belt around Donegal Bay. 



3. Glengesh Plateau. 



4. Derryveagh and Glendowan Mountains. 



5. Errigal-Muckish Eidge. 



6. Eosses and Bloody Foreland. 



7. Iforthem Peninsulas. 



8. Yalleys of the Finn and Foyle. 



9. Inishowen. 



10. Sperrin Mountains and Foyle Estuaiy. 



11. Bamesmore granite boulder dispersal. 



12. South-eastern area. 



