218 Proceedings of the Royal Irish Academy. 



others, liave elsewhere been used in the doh'mitatioii of the earlier and later 

 glaciations, lias rendered it well-nigh impossible to fix the limits of the earlier 

 Scottish glaciation in such places as, for example, at the head of the 

 Glenshane Pass and in the headwaters of the Eiver Eoe. 



Most of ilie striae in the area east of the Foyle estuary are attributable 

 to the later Donegal glaciation, e.g. those observed on Ihe summit of 

 Loughermore and the striated surfaces on Benevenagh, bearing roughly 

 N.-N.-W. The prevalent direction is a little wi?st of norili, with an occasional 

 tendency to swing more to the westward under tiie restraining influence of 

 the relief, though this deviation may be in part due to the reaction of the 

 western with the Scottish Ice, which was occupying the country to the east.' 

 In the Eoe Valley, boulders and pebbles of basalt predominate in the drifts 

 near the great escarpment, decreasing gradually in size and numlicrs as the 

 distance from the escarpment increases, and becoming rare, with a distinct 

 preponderance of metamorphic rocks from the Sperriii Mountains and their 

 foot-hills, in the drifts of the valleys west of the Eoe. As already pointed 

 out by J. E. Kilroe,- one of the most interesting pieces of evidence of the 

 northward movement in this area is to be found in the valley of Largantea 

 Burn, to the east of Benevenagh, where chalk fragments, doubtless gathered 

 up from the outcrop north of Keady Mountain, are strewn along the stream 

 course up to its head waters, though in decreasing quantities as traced away 

 from the place of origin. Chalk-flints, less destructible and perhaps more 

 easily recognisable, have been picked up on tbe highest ground thereabouts, 

 while metamorphic grit was found at the summit of Benevenagh (1,260). 

 Portlock (" Eeport," p. 638) writes in this connexion : — 



"On ascending the steep sides of Benevenagh, fragments of quartz 

 and pebbles of mica-schist are found in the beds of the small streams, 

 mixed with chalk and trap pebbles, and continue nearly to the summit 

 of the mountain." 



The striated surfaces on Benevenagh and these small patches of stoiiy 

 boulder-clay, traceable to within very short distances of the highest summits 

 along this north-west edge of the Antrim plateau, prove, without doubt, that 

 this elevated tract was buried to some depth below a northwaid-moving 

 ice-sheet. 



As already pointed out by Mr. W. B. Wright," this northward movement 



' In agreement with these N.-N.-W. striae <jii Benevenagh is the occurrence of great 

 numbers of hirge bouklers (3 feet) of basalt, some amygdaloidal, and dolerite along the 

 cliff road from Inishowen Head to Glenane Hill and over the low ground to tlie S. of the 

 former. 



- Belfast Nat. Field Ckib, 1913, p. 653. » Quaternary Ice Age, p. 60. 



