part 3] GLACIATION OF NORTH-EASTER IRELAND. 4011 



A much larger and more definite channel runs in a north-easterly- 

 direction from the eastern end of Lough Island Beavy, by way of 

 Altnadua Lough, to the valley of the Bun-en Biver near Castle- 

 wellan. The stream which now flows through this valley is only 

 3 feet wide, and is almost choked with grass and other vegetation,, 

 whereas the floor of the valley is wide and swampy and is nearly 

 level, though with a slight fall towards the north-east. 



The valley of the Bun-en Biver below r the point where this, 

 channel enters it is very wide, has a flat floor, and is out of all 

 proportion to the size of the river. 



The comparatively low-lying country between Lough Island 

 Beavy and Bathfriland, and thence onwards to the Newry Valley, 

 is covered hj mounds of drift, among which are numerous small 

 lakes and peat-bogs occupying hollows in the drift. 



The Mourne Mountains. 



Under this head will be described that part of County Down 

 which lies south of the Castlewellan-Hilltown-Newry road. 



An examination of a contoured map will show that south of that 

 portion of the road which lies between Hilltown and Newry is a 

 triangular hilly area based upon the road, having its apex at the 

 head of Carlingford Lough, bounded on the south-west by the- 

 steep mountains of the Carlingford Bange, and on the south-east 

 by the Mourne Mountains. 



The evidence of the extreme severity of the glaciation to which 

 this triangle has been subjected is to be seen on every hand, 

 in the general form of the country, in the frequency of roches- 

 moutonnees and striated surfaces, and in the enormous overflow- 

 channels by which the country is intersected (see map, fig. 7, 

 p. 406). 



The interpretation of the glacial phenomena of this triangle is a 

 comparatively simple matter, for, although it was covered first by 

 the Scottish ice and later by that from the north-west, the lower 

 layers, at least, of both these sheets Avere constrained by the form of 

 the ground to flow southwards, and to find escape through the 

 narrow opening between the Carlingford and Mourne Mountains, 

 now occupied by the fiord of Carlingford Lough. 



Carlingford Lough, in fact, owes its existence very largely to the 

 erosive power of the glacier ; and it is a point of great significance 

 that the narrowest portion of the Lough, where it cuts through the 

 mountain -barrier, has the most precipitous sides and is of greater 

 depth than any other part. 



Running down the centre of the Lough from opposite Killowen 

 to a point 1 mile north of Greenore, is a deep channel round which 

 the 5-fathom line forms a closed contour. In the narrowest part 

 of the valley, where the ice-scour was necessarily greatest, the 

 bottom of this trough descends below the 15-fathom line, a depth 

 which is not again reached within 5 miles of the coast (see fig. 8, 

 p. 408). 



From Greenore to the actual mouth of the Lough is another 



