part 3] GLACIATION OF NORTH-EASTEW IRELAND. 403 



by the drainage of Lough Neagh during the retreat of the western, 

 ice, while the Belfast Valley and that of the Lower Bann near- 

 Castlerock were still closed by the Scottish ice. 



The problem of the pre-Glacial drainage of the Lough Neagh 

 Basin is an extremely interesting one ; but, before anything definite 

 can be said on this subject, or on the cognate one of the origin of 

 the existing drainage-system, a much closer study of the sub-drift 

 contours than is at present possible must be made. 



To return now to the drainage-channels of the Newry-Hilltown- 

 Warrenpoint triangle. There is a veiy large flat-floored valley 

 running parallel to, and about a mile east of, the Newry Valley. 

 It contains Greenan Lough, and several other small lakes and 

 swamps. The watershed in this valley is at about 110 feet, and its 

 northern end is crossed at right angles by the Newry River at a 

 level of 105 feet. At its southern end the channel deeply notches 

 the 100-foot contour, and enters the Newry Valley opposite Narrow 

 Water Castle. 



Another, large parallel channel at a higher level (320 feet) runs 

 between Bullock Hill and the southern spur of Craignamona. It 

 contains Milltown Lough, falls towards the south, and is streamless 

 in its upper part. 



Other channels occur on the north-western flank of Craignamona 

 at 590 feet, and between Slieveacarnano and Bally vally Mountain 

 at 612 feet : both these fall southwards. 



The two great parallel valleys (through which pass the two roads 

 from Hilltown to llostrevor) lying between Slieveroosley and 

 Corlieve Mountain, and between the latter and Tievedockeragh 

 respectively, and cutting through the watersheds, are much encum- 

 bered by drift and peat, but must have carried great volumes of' 

 water from the Hilltown area southwards to Carlingford Lough. 



The Mourne Mountains consist, for the greater part, of granite 

 of Tertiary age, although the summits of several of the highest 

 peaks in the western portion are capped by masses of altered 

 Silurian strata — the relics of the cover of the granitic laccolite. 



These mountains form a detached group, which stood in the track 

 of the Scottish ice that swept over County Down, and were to a 

 considerable extent overwhelmed by it. Striae occur up to and 

 slightly above the 1500-foot contour on Pigeon Bock Mountain, 

 and the plateau of Silurian rocks which forms the summit of" 

 Slievemuckamore (1837 feet O.D.) is littered by thousands of 

 granite -boulders carried from at least 250 feet below. 



Whether the higher summits, such as Slieve Donard (2796 feet), 

 and Slieve Bignian (2449 feet), were covered by ice is largely a 

 matter of conjecture ; but their rounded outlines, and the fact that 

 Snaefell in the Isle of Man (2062 feet) was overridden, make it 

 reasonable to suppose that such was the case. 



Bunning westwards from Slieve Donard is a line of peaks forming 

 the northern rampart of the group — Slieve Commedagh (2812 feet),. 



