OVERLYING ROCKS OF ROSS AND INVERNESS. 



155 



9. Loch Shiel to Caledonian Canal (fig. 4). 



In figure 4 I show the general arrange- 

 ment of the rocks between Glen Finnan, at 

 the head of Loch Shiel, along the north shore 

 of Loch Eil to the Caledonian Canal. The 

 more highly crystalline rocks are well seen 

 in the mountains about and directly to the 

 east of Glen Finnan, as well as along the 

 roadside. I ascended one of these moun- 

 tains, called Ben Nan Tom, and found it to 

 be composed entirely of massive-looking 

 gneisses, frequently hornblendic, and con- 

 taining lenticular segregations and bands of 

 hornblende, of a reddish and light-coloured 

 felspar mixed with quartz, and of black mica. 

 The hornblendic bands are described in note 

 22, and the gneisses from this point in note 

 23 of the Appendix. The rocks are beautifully 

 contorted in places, and the strike in the folia- 

 tion is fromN'.W.to S.E., orvarying from that 

 to N. and S. In many respects these rocks are 

 much like those found between Poolewe and 

 Gairloch, on the west coast ; and it seems 

 impossible to conceive that they can be, as 

 suggested by Murchison and Geikie, only 

 Silurian beds in an altered and crumpled 

 condition. The interpretation as given by 

 them occurs in the following passage : — 

 ;< We have shown that the quartz-rocks and 

 limestones of Sutherland range south-west- 

 wards through Ross-shire into the Isle of 

 Skye, — that they are covered by a vast series 

 of micaceous flaggy or gneissose schists ; 

 that these are disposed- as a great synclinal 

 trough, the centre of which traverses the 

 head of Glen Shiel, the middle of Loch 

 Quoich, and the watershed of Glen Finnan, 

 — and that, by the curving of this trough, 

 the quartzose beds which form its outer or 

 lower edge along the western coast at 

 Arisaig are brought up again along the 

 line of the Great Glen"*. The highest 

 beds are therefore placed by them at the 

 point where we meet with the most highly 

 altered rocks ; and the least altered mica- 

 ceous flaggy beds and the unaltered rocks 

 are placed at the baso of the trough to reach 

 the surface along the line already described 



* Quart. Journ. Geol. Soc. vol. xvii. p. 207. 



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