ROCKS OF THE NORTHERN HIGHLANDS. 393 



cores of Hebridean gneiss, but no more constituting the mountain 

 it encloses than if it were a permanent mantle of snow or ice. 



The western mountains, consisting of Torridon sandstone capped 

 by the quartzite, have already been described by authors. My 

 observations refer chiefly to the Ben More mass and the ranges 

 which radiate from it. 



Scounan More. — Usually regarded as " igneous," but by Dr. 

 Heddle as " Logan Rock.''* It is a mass of nearly vertical Hebri- 

 dean. On the south-eastern slope a film of quartzite dips down 

 towards Loch Ailsh. 



Brebag (2670 ft.) (fig. 5, p. 380).— This linear mass, striking N. 

 and S., continues the Scounan ridge onto Ben More. It is entirely 

 swathed in quartzite, which is compressed into a sharp anticline 

 along the summit, with gentler curves on each side. On the western 

 slope the folds are closer than on the east, and are overthrown. This 

 quartzite thus resembles a wave blown along by an easterly wind, 

 the slope on the east side being gentle, while on the west the 

 crest falls over. This structure is another proof of the action of 

 the lateral force from the east which produced the striking effects 

 already described. 



Ben More (3273 ft.). — We have seen that the old gneiss rises to 

 2500 feet in this mass, the capping being of the quartzite with the 

 Ben More grit and conglomerate at its base. The great spur 

 which projects to the south nearly halfway to Loch Ailsh is nearly 

 all gneiss, a thin sheet of quartzite resting only on the highest parts, 

 as described on Eagle Rock, which terminates the massif on the south. 

 The precipitous western escarpment of Coniveall is also covered in 

 by quartzite — not, however, in sheets plunging down to the west, 

 but in beds dipping gently into the mountain. Ascending from 

 this side, there is therefore the appearance of a great thickness 

 of quartzite. That these strata are broken off is certain ; for we 

 know that the gneiss passes through the middle of the mass to 

 within 500 or 600 feet of the summit. Nothing but a knowledge 

 of the minute differences visible within the quartzite series would 

 here help us to a solution. 



The following facts were seen in ascending the Traligill to the 

 col between Ben More and Ben Uarran. At the foot of the cascade 

 (925 ft.) is a considerable thickness of the Brown Flags, succeeded 

 by quartzite, and at 1100 ft. by dolomite. There is no great thick- 

 ness of this ; and at 1175 ft. quartzite of the annelidian type comes 

 in. Towards 1475 ft. the quartzite rises gradually to the vertical, 

 and is thrown over, the seamy bands being uppermost; and rock of 

 this variety occupies the scarp up to the pass (2025 ft.). Intrusions 

 of igneous rock have been frequent from near the base of the section 

 to this point, some of the masses being of considerable thickness. In 

 some places the igneous rock is interbedded. The dip of the quartzite 

 has been easterly at a low angle. "With the key already furnished 

 to us, the explanation of these facts is not difficult. I am satisfied 

 that the Balloch fault passes round the face of Coniveall, and that 

 in the section just described the quartzite is thrown down against 



