400 MAJOB A. E. DWEBBl'HOTTSE ON THE [vol. lxxix, 



Striatums exposed during the building of the railway between 

 Bannbridge and Dromore, and recorded by the officers of the 

 Geological Survey, also indicate a movement from north-west to 

 south-east. 



Near Grarvaghy, some 4 miles east of Bannbridge, are two- 

 large overflow-channels falling south-westwards and southwards 

 respectively. They contain much peat and several boggy pools. 

 The larger and northernmost of these channels is some 3 miles 

 long, and its intake is at about 340 feet. I consider these to have 

 been formed during the earlier northern glaciation, but their 

 relationships are somewhat obscure. 



On entering the hilly country along the northern edge of the 

 granite intrusion we find the drift deposits to be much thinner 

 than those in the low ground, and here the effects of the south- 

 eastward movement are unmistakable. During the retreat tem- 

 porary lakes were formed between the ice-front and the sides of' 

 the northward-falling valleys of the range, and their waters 

 flowed southwards across the cols, cutting numerous channels. 

 Some of the largest of these are between Deehommed Mountain and 

 Slievenaboley, between Slievenaboley and Cratlieve, and between 

 Cratlieve and Slieve Croob, where there are two parallel channels. 

 There is also a channel falling south-eastwards between Slievenisky, 

 the southern spur of Slieve Croob, and Slievegarren. 



The larger channels of this range were doubtless produced during 

 the northern glaciation, and again occupied by streams during the 

 glaciation from the west. 



In this area are many boulders of local granite in the drift, also 

 numerous erratics of Silurian grits and slates, and pebbles of flint 

 derived from the north-west. I have been unable to find the 

 igneous rocks of the Tyrone Axis ; but, in such a profusion of 

 granitic debris as occurs here, they would, even if present, be very 

 difficult of detection. 



Southward from Slieve Croob to the neighbourhood of Lough 

 Island Beavy runs a ridge of hills, the craggy summits of 

 which reach heights of from 700 to 1000 feet. This ridge lay 

 athwart the path of the western ice, and on all hands are to be 

 seen signs of the severe abrasion to which the rocks were subjected 

 during its passage. Thus on Curlets Mountain, which consists in 

 part of granite, and in part of highly metamorphosed Silurian 

 rocks, the former is worn into rounded bosses, and the latter are 

 extensively striated. 



North of Curlets Mountain lies a broad valley, which cuts through 

 the range at a level of about 330 feet, and has evidently carried a 

 much larger stream than that which occupies it at present. It falls 

 eastwards, and carries the railway between Leitrim Station and 

 Castlewellan. 



South of Curlets Mountain the ridge is cut by r.umerous small 

 notches, which Avere produced when the ice stood against the 

 western side of the ridge, but was no longer able to overtop it.. 

 Several of these notches drain into the hollow now occupied by 

 Castlewellan Lake. 



