CiiARLiiSWoETH — Olacial Geology of North- West of Ireland. 309 



phase, would seem to prove the shortness, or possibly entire absence, of a 

 late-glacial corrie period, and the rapid melting of the ice and passing away' 

 of glacial conditions. 



Slieve League is only a partial exception to these general statements. Its 

 two recesses, the one on the northern flank and containing Though Agha, the 

 other on the southern side, with Lough Croleary nestling in the bottom, are 

 rejuvenation features, which were occupied in early- and possibly in late- 

 glacial times by corrie glaciers. Above the wide cirque on the southern side 

 extends a fairly sharp, steep-sided and serrated ridge, the " One Man's Pass," 

 the one ridge to be found in Donegal which even remotely resembles an 

 Alpine arrete. The presence of this feature is to be explained by the fact 

 that Slieve League, though buried under its own ice, was probably never 

 completely overridden by extraneous ice. The asymmetry of the ridges, 

 noticeable in countless cases in Donegal, is only in small measure to be 

 ascribed to glacial erosion, as desk-structure has played a far more important 

 role. 



The preceding considerations suggest glacial erosion on only a moderate 

 scale. Uncertainly as to its amount is introduced by inability to give a 

 value for the glacial degradation of the coastal peneplain, and by the great 

 difficulty of ascertaining the pre-glacial gradient of the valleys originally 

 accordant with this feature. 



That glacial erosion under certain conditions is almost negligible is 

 suggested by the cross-striations on Croaghleconnell, also by the preservation 

 of the striae on Doagh Island, which have been regarded as relics of the 

 earlier Scottish glaciation. The preservation intact of an older drift in the 

 valleys south of the Foyle estuary, despite tlie passage of the Donegal Ice, 

 worrld seem to confirm this view. 



Of true fiords there are in the north- west of Ireland but two— Mulroy Bay 

 and Lough Swilly. Though they are comparatively shallow features, the 

 distribution of their depths demonstrates glacial modification. 



Mulioy Bay is practically an inland lake, connected with the sea by a 

 tortuous channel which, between the peninsulas of Eosguill and Fanad, is 

 9 fathoms deep, though on the seaward side its maximum depth decreases 

 to 2 fathoms. It likewise shallows southwards towards the Narrows, where 

 it is only some 350 yards across, and 2 fathoms deep. Farther up, where the 

 inlet widens, the floor again sinks to 14 fathoms (N.-E. of Cranford). A deep 

 pool of 10 fathoms lies still farther south (S.-W. of Carrowkeel), and is bounded 

 on the north by a ridge covered by only 2 fathoms of water. 



Though drift undoubtedly obscures the real depth to the rock-floor, the 

 deeper parts most probably represent true rock basins scooped out by 



