﻿1861.] 



HARKNESS HIGHLANDS AND N. IRELAND. 



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varying thickness, and in some instances appear to thin out alto- 

 gether ; and are succeeded by, thirdly, the gneissose rocks, which 

 occupy so great an area in the Highlands of Scotland. 



§ 7. Sections N. W. of the Great Zone of Quartz- 

 rocks and Limestones. Section from Glen Lyon 

 to Loch Treig (fig. 6). — Allusion has already 

 been made to the black gneiss which is seen 

 having a S.E. dip in the north side of the quartz- 

 rock zone at Inverwick. In Glen Lyon, rocks of 

 this nature, and with only slight modifications in 

 their dip, extend themselves to the western end 

 of Loch Rannoch, where an extensively deve- 

 loped area of syenite occurs; and from this syenite 

 the gneissose rocks usually incline south-eastward 

 in the neighbourhood of this lake. 



The area occupied by this syenite, as shown in 

 geological maps, fails to afford anything like an 

 adequate idea concerning the extent of country 

 which this rock covers. Erom the head of Loch 

 Rannoch it extends along the mountain-road lead- 

 ing to Fort Wiliiam — at least as far as Loch Ou- 

 chan, and from this, westward, almost to Loch 

 Treig ; but its area was not definitely determined. 

 In the form of a flesh-coloured porphyry, this 

 plutonic rock occurs in all the streams which 

 drain the hills lying N. and S. of Uise-dhu, and 

 the lakes through which this stream flows in its 

 course to the Leven. This great plutonic area, 

 coloured as gneiss in geological maps, seems to 

 abut against the trap-rocks of Glen Coe. 



At the head of Loch Treig we find it flanked by 

 gneiss, which dips N.W., or from its S. margin, 

 as at Loch Rannoch ; the same rock inclines S.E. 

 from its southern boundary. 



§ 8. Section from King's House, through Glen 

 Coe, to Ballahulish (fig. 7). — The plutonic rocks 

 just referred to extend to King's House ; but on 

 passing westwards towards Glen Coe, the dark 

 porphyries and trap-rocks which exclusively fill 

 this gorge, soon make their appearance. They 

 occupy the whole of the glen to Claichig, where 

 we have stratified rocks coming abruptly against 

 the traps, as seen on the hill-slope immediately 

 opposite the small inn at Claichig. 



These stratified rocks dip W.N.W. at 45°, and 

 they have somewhat of a gneissose aspect, but are 

 much more highly siliceous than ordinary gneiss. 

 Macculloch alludes to their differingfroni mica-slate, 

 and designates them schistose " quartz-rocks*." 

 * Geol. Trans, vol. ii. p. 475. 



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