﻿I860.] 



NICOL N.W. HIGHLANDS. 



99 



that of Queenaig and Suilven. In the corries of Ben More similar 

 beds occur, resting on gneiss or mica-slate (as shown in the section) ; 

 and there can be no doubt that this is the true western Red Sand- 

 stone (" Cambrian " of Murchison) brought up in the centre of the 

 so-called " upper quartz-rock," and that the synclinal is thus com- 

 plete in all the formations from the upper limestone to the lowest 

 gneiss. 



The eastern extremity of the section shows the true structure of 

 Ben More, as exposed in the wild corries round the Dhu Loch More. 

 Granitic gneiss and mica-slate, with intrusive igneous rocks, form 

 the nucleus of the mountain, throwing off the quartzite all around, 

 as from a great centre of elevation. Further west an enormous 

 mass of beautiful binary granite rises into a group of rugged moun- 

 tains, quite unlike the quartzite with which they have hitherto been 

 confounded*. Taken in connexion with the Loch Borrolan por- 

 phyry, with which it is probably continuous, this granite must pro- 

 duce most powerful disturbance along the south-east border of the 

 quartzite ; and we can easily understand how observers who ignored 

 or overlooked its existence should mistake the true relations of the 

 stratified rocks it has affected f. 



Loch AilsJi Section. — It is, again, affirmed that in the vicinity of 

 Loch Ailsh and the higher part of Strath Oykill, the " upper quartz- 

 rock " forming the Assynt mountains " is overlain by a second zone 

 of limestone," and both " conformably surmounted by upper mica- 

 ceous, chloritic, gneissose, flaggy strata. . . .'for several miles across 

 the strata*." My examination of the locality last summer (1860) by 

 no means confirms these views. The " upper quartz-rock " is simply 

 the continuation of the quartzite of Brebag and Canisp, and the 

 " second zone of limestone " merely the repetition, in a denuded 

 form, on the other side of the anticlinal, of the limestone of Stron- 

 chrubie and Assynt. Any slight change in the colour or character 

 of the strata is readily accounted for by the intrusion of the red 

 porphyry of Loch Borrolan, which probably at no great depth under- 

 lies the rocks shown in the section (fig. 9). 



This section begins on the west, at Cnoc Chaorinie, with a hard 

 reddish or clove-brown hornstone-porphyry (x) with distinct cry- 

 stals of felspar, but probably only a semifused mass of the quartzite. 



* In justice to Mr. Cunningham, it must be stated that the greater portion of 

 these granite mountains lie in Ross-shire, and thus beyond the limits of his map. 



t In the Quart. Journ. Geol. Soc. vol. xvi. p. 232, it is stated that " no ig- 

 neous rock has yet been observed to be associated with the lower quartz-rock of 

 Assvnt ;" and that the " large crystalled porphyry " of Canisp may be considered 

 "for the present to be characteristic of the Cambrian age in the North-western 

 Highlands." In 1859, 1 found that this very beautiful porphyry not only breaks 

 though the quartzite of Canisp, but forms a mass more than a mile in diameter 

 .in the same " lower quartz-rock," within a few hundred yards of the inn of Inch- 

 na-Dam£f. It is thus of later date than either the Eed Sandstone or Quartzite, 

 and is one of those powerful agents affecting the relations of these and the other 

 strata which have hitherto been overlooked. 



I Sir It. I. Murchison, "Supplemental Observations on the North of Scot- 

 land," Quart. Journ. Geol. Soc. vol. xvi. p. 223. 



H 2 



