214 Proceedings of the Royal Irish Academy. 



m 



In the part of Donegal described in this section, the ice sweeps out a 

 complete quadrant, in the south passing almost due west, in the north 

 practically due north. 



7. The Northern Peninsulas. 



The northern peninsulas were glaciated by ice which swept northwards ; 

 the Ards peninsula from S. 10° E., and Eosguill from S. 20° E. 



The ice which crossed Barnes Gap and overflowed Crockmore, situated to 

 the north of that valley, proceeded somewliat obliquely across Glen Lougli ; 

 the glaciers from Salt Mountain and the area to the immediate west passing 

 in a parallel direction over Bunbin and Cook's Heath Hill. 



Salt Mountain and otlier hills of the Salt i-idge show most clearly their 

 glaciation from tlie south. Glaciers poured down from their heiglits in a 

 direction slightly west of north, so tliat quartzite erratics derived from these 

 sources lie scattered in great profusion over all the country to the north and 

 west of the range. 



The outcrop of the Fanad granite is beautifully moulded into well-rounded 

 bosses, demonstrating a south and north ice-flow. "No boulders of either the 

 Kosguill or the Fanad granite were observed south of the soutlievn margin of 

 their outcrops. 



The ice filled the loughs of Swilly and Mulroy Bay, conformed with tlieir 

 direction in its flow, as tlie map renders immediately apparent, and overrode 

 the summits of the Fanad penin.sula. 



Probably in the earlier stages of the glaciation of the area, the ice was 

 split on the great ridge of Knockalla. The presence of striae on the summit 

 of the ridge conclusively proves, however, that the latter was finally swamped 

 under the great ice-sheet. 



The distribution of the boulders of the Donegal granite may be here 

 briefly reviewed ; the dispersal is illustrated in the small map (fig. 1), upon 

 which are also inserted the lines of ice-flow over this part of Donegal. 



Granite boulders occur in great profusion over the outcrop of the Donegal 

 granite ; these require no further description. They were observed in the 

 metamorphic country to the soutli of Ardara, their occurrence here being due 

 to slight " nudging." They are also plentifully distributed over the low 

 peninsula terminating in Loughros Head, and over that which juts out to 

 tlie south of Gweebarra Bay, while they occur over all the Crohy peninsula to 

 the north of this bay. As already mentioned, they are found in the north- 

 western part of Aran Island. 



The roughly rectangular tract of countiy underlain by metamorphic and 

 associated rocks and bounded on the west, south, and east by the granite of 

 the Bosses and Derryveagh, is everywhere bestrewn with granite boulders of 



