﻿I860.] 



NICOL N.W. HIGHLANDS. 



Ill 



quartzite, throwing it over in large fragments to the S.E., indepen- 

 dent altogether of the present strike or dip of the heds. This is 

 clearly shown on the west side of Loch Emboli, where the quartzite, 

 with the inferior gneiss-platean on which it rests, have both a dip 

 to the S.E. This is also true of the great plateau of gneiss on which 

 we must suppose the quartzite of Eoinaven and Arkle, now dipping 

 at 20° to the S.E., to have been laid down in nearly horizontal 

 masses. So also on Loch Maree and Loch Carron, there is evidence 

 of the upturn of the formations in enormous fragments. Further 

 east, the same overthrow of the masses from the JNT.W. is evident in 

 the form of the hills and in the position of the newer formations of 

 the east coast. The cause of this most remarkable convulsion must 

 be sought in some more powerful agent than any of the masses of 

 igneous rocks now visible on the surface in this part of Scotland. 



Mineral character, — The diversity in the mineralogical character of 

 the rocks has also been often alleged in proof of the overlap of the 

 eastern gneiss. Now it must be stated that, though Dr. Maceulloch 

 coloured the whole of central Sutherland as gneiss, yet Mr. Cunning- 

 ham recognized that some portions of it were mica-slate ; and the same 

 distinction appears in subsequent maps. In comparing the gneiss of 

 the east with that of the west, such mica- and chlorite-slates must 

 of course be" set aside, though it is undoubtedly true that they are 

 quite as crystalline in texture, and as distinctly separated from 

 the true sedimentary formations, as the gneiss. In regard to the 

 gneiss itself, Mr. Cunningham, undoubtedly both a competent and 

 an unprejudiced observer, states that " the mineral characters of 

 both " (the eastern gneiss, which he believed to overlie the quartzite, 

 and the western, which underlies it) " are essentially the same*," 

 and expressly affirms that " he has never found any indications of 

 mechanical action on its individual constituent minerals f." It is 

 no doubt true that " hornblendic varieties of gneiss are very cha- 

 racteristic of this formation in the west of Sutherland %; " but the 

 more usual kinds also occur, and in the Gairloch district its general 

 aspect " is a light or dark grey, finely granular rock, interstratified 

 with beds of mica-slate §." In Far-out Head, again, it is a true 

 mica-slate, identical in mineral character (as it is also in dip and 

 direction) with that on Loch Hope and the Kyle of Tongue. 

 On the other hand, rocks quite as hornblendic and as thoroughly 

 granitic in character are common in the eastern gneiss-district. 

 Such rocks may be seen near Strath Naver, Strathie Point, and on 

 the borders of Caithness in Sutherland ; at Auch-na-Sheen and Loch 

 Carron in Ross-shire, and at Glen Elg and Isle Oronsay in Skye in 

 Inverness. Further east, in Banff-, Aberdeen-, and Kincardine- 

 shires, they are perhaps the more common varieties. In truth, 

 this peculiar character of the rock has no relation whatever to its 

 age or locality, but only, it would appear, to its proximity to the 



* " Geog. of Sutherland," Trans, of Highland Society, vol. xiii. (1839) p. 101. 

 t lb. p. 78. 



\ Nicol, " Quartzites of N.W. Scotland," Quart. Journ. Geol. Soc. vol. xiii. 

 (1857) p. 24. § lb. p. 28. 



