216 Proeeedings of the Royal Irish Academy. 



become inereasingly numerous aud lai-ge uutil they reach their gieatest 

 numbers near Carrigarfe as already mentioned. 



In that part of Fanad lying to the south-west of Eindrum Lough, veiy 

 few boulders from the main Don^al outcrop were obsenred, their detection 

 and recoguition beiug made the more difficult when they pass on to the out- 

 crop of the northern granites, where indeed they are practically lost among 

 the countless local granite erratics. 



8. The Valleys of tJie Finn and Foyk. 



The ice passed in general down the valleys of the Finn aud Foyle. Tliis 

 is proved by the striae {viAe map), by the transport of erratics, eg. the 

 Barnesmore granite, quartzites, "and the diorites and lime-stones occuning 

 north of ihe Finn valley, and by the low driunlinoid motmds. 



The drumliu ridges in the " Pennybixm depression " west of Londonderry 

 swing into the Foyle in wide parallel curves, in striking conformity with 

 the line of the Ijounding hills on the north. Their aiTangement indicates the 

 wheeling of the ice i-ound the southern shoulders of Scalp aud Eskaheen 

 Mouutaius. The numerous striated surfaces on the rocks to the north of 

 the depression, bearing generally N. 50° to 70" E., show also the effect of 

 the great Scalp Mountain range on the lower currents of ice. Though these 

 markings and mounds were most probably produced during the maximum 

 stage, they may be in part the product of late glacial times, when the ice 

 i-etreatiug oflf Inishowen was so reduced in strength and thickness as to be 

 unable to surmount this high range, aud formed two powerful glaciers, the one 

 streaming down the Swilly, the other filling the " Pennybum depression " 

 from side to side and skirting the southern edge of this i-ange of mountains 

 aud subsequently flowing into Lough Foyle. 



9. Inishoicen. 

 The general direction of glaciation over Inishowen was northwards, the 

 striae ' bearing steadily south-north, though local deflections due to the relief 

 were noted, as along the big depression of the Swilly where the striae indicate 

 the winding of the glacier in agi-eement with the S-shaped curve of the fiord, 

 while the huge valleys of Glentogher and the iliniiaghs guided the niovement 

 of the ice in these regions. The distribution of the surface erratics and of the 

 drift material that thickly drapes the flanks of the lulls, e.g. the diorites of 

 the Mintiaghs and Buncrana and the quartzites of Slieve Snaght, the 



* Reference to manx striations iu Inishowen is made by Maxwell Close in his 3f otes 

 on the General Glaciacion of Ireland, Joum. Roy. Geol. Soc. Ireland, vol. i, p. 217, and 

 by CarriU Lewis, op. eit., pp. 110 to 116. 



