378 MAJOR A. R. DWERimiOUSE OS THE [vol. lxxix, 



That the main flow of ice in the later stage of the giaciation, 

 in the Moneymore, Cookstown, and Magherafelt area, was north- 

 eastward is shown by abundant evidence, both in the transport of 

 erratics and in the distribution of the overflow-channels. 



There are numerous small dry gaps, all falling north-eastwards, 

 in the neighbourhood of Windy Castle, a spur of Slieve Gallion. 

 The highest of these channels is at 1300 feet above Ordnance 

 datum. 



At lower levels, between 200 and 400 feet, is a series of veiy 

 broad channels, which were formed along the edge and probably 

 near the termination of the much shrunken glacier at a later stage, 

 when, however, the ice was still flowing northwards in this district. 

 These channels are marked in fig. 5 (p. 376), and they are cut 

 partly in the solid rocks of the district, and partly in drift. Often 

 the outer side, away from the ice, is of rock, while the inner is 

 of boulder-clay and gravel ; but the channels all have the typical 

 form of glacial drainage-gaps, being deep, steep-sided, flat-floored, 

 and altogether out of proportion to the streams which now flow 

 through them, many being actually streamless. 



The two largest of these channels are Carndaisy Glen and 

 Gortanewry Glen. In addition to the drainage from the ice, the 

 great gorge of Carndaisy Grlen must have carried all the water 

 from that part of Slieve Gallion which lies between Clagan Rock 

 on the south-west and Carndaisy on the north-east: that is, the 

 townlands of .Dirnan, Derryganard, Letteran, and Tintagh ; and at 

 one stage the same waters flowed through Crortanewry Grlen, 

 although at a later stage they escaped into the low ground in 

 the neighbourhood of Pough Hill. All these channels were 

 tributary to a very large northward-flowing stream which cut a 

 broad channel, now occupied by the railway between Magherafelt 

 and Moneymore, along the foot of the basalt escarpment. 



The basalt country between the railway and the western shore of 

 Lough Neagh is covered by mounds of gravelly drift, and both the 

 axes of the mounds and the striations on the basalt indicate a 

 north-north-eastward flow. Over the whole of this area are scat- 

 tered boulders of the Lissan granite and other rocks from the 

 Slieve Gallion complex, showing that the ice which passed over it 

 came originally from the west, but was deflected northwards and 

 north-eastwards. This deflection and its cause will receive further 

 consideration later. 



The country between Monejanore and Cookstown is covered by 

 mounds of gravelly drift containing abundant western erratics. 



In the latitude of Cookstown the Ballinderry River cuts through 

 the basalt escarpment at Coagh, and flows by a narrow valley into 

 Lough Neagh. I am of opinion that this gap in the escarpment 

 owes its origin to glacial drainage, although actual proof of this is 

 not forthcoming. If this surmise be correct, the glacial waters 

 would at this stage abandon the Moneymore-Magherafelt channel, 

 and find exit by this shorter route to the lough. 



