122 



KNOWLEDGE 



[June 1, 1898. 



but it has, when mapped out, a fairly north-east and south- 

 west trend. A bold line of summits lies along it, from 

 Slieve Meel More to Eagle Mountain ; but their average 

 elevation is surpassed by those rising from the wall 

 between the Annalong and Kilkeel valleys, beginning 

 with Slieve Commedagh (2512 feet), and ending in the 

 castellated crags of Slieve Bingian (2449 feet), from 

 which a long spur descends southward on Kilkeel. The 

 depth of the valleys, in proportion to their width, is one 

 of the fine features of the Mournes, and is only fully 

 realised by walking along the watershed, and looking down 

 over granite cliffs into these veritable grooves, the combes 



According to this view, the domes and valleys of the 

 Mourne Mountains have been carved out of an obstacle, 

 discovered by the agents of denudation on the side of an 

 older ridge. The former covering of Silurian strata is 

 actually left to us in a few admirable outliers — a patch 

 half a mile across on Thomas Mountain, about half way 

 up Slieve Donard ; another on Slievemaganmore, midway 

 between Hilltown and Kilkeel, at a height of 1830 

 feet ; and another, fifty feet higher, on Finlieve, some 

 three miles to the south. It has been stated that 

 these fiakes of strata have been floated up on the 

 surface of the invading granite ; but the Silurian beds 



Fia. 1. — View in the Valley of tlie lulkeel River, Mourue Mountains, showing cliff, taluses, and distant summits. 



Bernagh is on the right. 



The peak of Slieve 



[R. Wdch, Photo. 



at their heads girt about with crags, and their mouths 

 crossed by the blue horizon of the sea. 



The north-and-south trend of the valleys is not due to 

 any special structure of the Mournes, for it is one common 

 to the district. So constant is it, whether the Mourne 

 granite, or the Silurian strata, or the older granite of the 

 Newry axis is traversed by the streams, that it probably 

 points back to a time when the rocks exposed at the 

 surface were more uniform in character, and when a 

 highland of Silurian and Ordovician strata concealed the 

 Mourne granite altogether. The watershed then may 

 have run east and west, and on its surface the streams 

 received a uniform trend. As they cut away this surface, 

 particularly in the region of their head-waters, they came 

 down upon the concealed granite boss, and worked against 

 that more slowly. At one point, the streams running 

 northward have found no granite as yet beneath them, 

 and have notched back the old watershed conspicuously, 

 forming the long valley leading over to Kilkeel. 



in situ reach 1940 feet upon Slieve Muck, and 2200 

 feet on Shanslieve, north of Slieve Commedagh, and may 

 thus easily, at no distant period, have covered the whole 

 area of the Mournes. 



Slieve Donard, in that case, would be one of the first 

 knobs to protrude through the slates and sandstones as 

 denudation had its way ; while the low south-western 

 portion of the granite has far more recently come to light. 

 The boldness of outline, and the existence of so many 

 contrasted domes and peaks (Fig. 1), point equally to the 

 modern character of the group. Granite masses readily 

 become worn down, in our climate, to round and uniform 

 moorlands. On a fine day an observer on the Hill of 

 Howth, near Dublin, has only to compare the outlines of 

 the old Leinster granite with those of the blue peaks of 



* The geological details are described in Traill, " Explanation to 

 Sheets 60 and 71," Geological Survey of Ireland (1878), and Hull, 

 " Explanation to Sheets 60, 61, and 71 " (1881) ; but recent advances 

 already necessitate some revision. 



