7 10 Proceedings of the Royal Irish Academy. 



of west. Also, a conspicuous drumlin ridge situated on the south side of the 

 island has its long axis similarly oriented, and the roches moutonnees which 

 occur at various elevations up to the 600-foot contour line all present their 

 ice-dressed surfaces towards the east. In like manner the orientation of the 

 drumlins at the head of Clew Bay indicate the same general direction of the 

 current, and the few striae observed in the rocks of this heavily drift-covered 

 country give confirmatory evidence that the general trend of the ice was 

 westwards from the central ice-axis. 



On examining the glaciated surfaces of the rocks of this district it was 

 noted that, at several localities, a second set of striae, occurring on the same 

 or adjacent rock-surfaces, crossed those that pointed westward at a fairly 

 wide angle. This phenomenon, occurring as it does alike on the northern and 

 southern side of the island, as well as on the southern shore of Clew Bay, 

 cannot be due to a temporary or local oscillation of the Central Irish Glacier, 

 but must be the result of a distinct transverse ice-movement. The latter, 

 however, cannot have been very intense, nor of very great duration, for the 

 grinding to which the rocks were subjected by the second glacier was not 

 sufficient to obliterate the traces of the previous glaciation. 



The following extract from the Geological Survey memoir 1 already 

 mentioned gives an account of the local district glacier which produced the 

 transverse striae and which brought along with it a not inconsiderable pro- 

 portion of the loose superficial material at present found on Clare Island : — 



" When the ice coming from the central snow-field diminished in mass, 

 the country round Clew Bay was invaded by a local district glaciei', fed by a 

 snow-field situated in the mountainous district west of Lough Corrib, with 

 probably, as suggested by Kinahan and Close, 2 the mountains on either side 

 of the pass of Mauni Con and the Twelve Bens as centre. From this ice-shed 

 (see sketch-map, Plate IV) a great glacier flowed north-westward into Clew 

 Bay, overwhelming the greater part at least of Clare Island in its course, sub- 

 merging the hill of Knocknaveen, but possibly not overtopping the mountain 

 of Knockmore. Another portion of the ice descending from the northern 

 side of the ice-shed flowed northward over the low ground into Killala Bay. 

 In confirmation of the foregoing theory of the glaciation of this region, an 

 examination of the drift on the southern shore of Clew Bay will show that 

 the deposit consists of two types of boulder-clay. On the shore of the bay 

 directly north of Louisburgh, a 30-foot section of drift may be seen which 

 clearly illustrates this twofold character of the deposit. The lower part of 

 this section consists of blue-grey boulder-clay, rich in scratched limestone, 



1 pp. 31-34. 



2 " The General Glaciation of Iar-Connaught and its Neighbourhood in the Counties of Galway 

 and Mayo" (1872), p. 12, 



