210 Proceedings of the Royal Irish Acadenifi. 



tliese lulls are somewhat lower than tlie alliLude of the highest granite 

 boulders on Errigal, a difference of two or three hundred feet, a vertical uplift 

 of tliis amount must have taken place in the comparatively short distance of 

 circa three miles. It is, however, possible that the ice flowing from Slieve 

 Snaglit (2,240), which would normally pass well to the south of Ei-rigal, was 

 subject to certain variations in its direction of flow, due to a process of 

 " nudging," causing some of the higher layers of the granile-laden ice from 

 this mountain to pass on to Errigal. Though this would involve no uplift of 

 the granite boulders, I am inclined to think their source lay at the head of 

 the Poisoned Glen rather than on Slieve Snaght, and that some uplift actually 

 took place. 



The overriding of Errigal (2,466) implies a thickness of ice of at le;xst 

 2,500 feet in this central area. With the waning of the ice, almost imme- 

 diately after the passing of the maximum phase, the summit of the peak 

 would project as a nunatak, the ice being probably piled up much higher on 

 the east or " stoss '" side than on the west or lee side. 



6. Tlie Bosses and Bloody Foreland. 



Glaciers streaming from that section of the ice-shed situated to the 

 north-west of the Barnesmore Hills flowed roughly westwards in the 

 direction of Glenties and the plain of Ardara, as is proved by the striae and 

 the occurrence of an occasional Barnesmore granite boulder. An ice current 

 also bearing a few granite boulders passed obliquely across the depression in 

 which lie the rock-basins of Lough Ea and Lough Maddv.' 



West of the Barnesmore Hills, the lines of flow gradually swing from the 

 east-west direction of the Stracashel valley to the south-west trend of the 

 Caraween, Cloghmeen and Binbane ridge. This more southerly ice then 

 proceeded soutli-westerly to Donegal Bay, while in a more westerly direction 

 it came against the obstruction oflered by Mulmosog ilountaiu, and being 

 deflected by the latter through east-west to something north of we^t, united 

 with the ice pouring out of the valleys near Glenties and swept in a direction 

 bearing roughly- N. 20° or 30° W. across the great irregular plain stretching 

 to the north of Ar-dara. Large and numerous granite boulders derived from 

 this area are scattered over all the metamorphic country to the south of 

 Gweebarra Bay and over the low peninsulawhichruns westward from Ardara 

 to Lougbros Point. The w-hole of this peninsula shows unmistakable signs 

 of severe glaciation from the east. On the diorite and schist, striae bearuig 

 W. "20° N. abound. Erratics of the local diorite are plentiful, though some of 



' Granites were observed among other places in the great accuniulatious of drift in 

 the bottom of the Onren River, above Martin's Bridge. 



