ROCKS OF THE NORTHERN HIGHLANDS. 361 



It was made up of a series of beds of the usual coarse sandstone with 

 intercalated thin bands of shale, the grit-beds being generally about 

 6-10 feet, and the shale from 6 inches to 1 foot." Mr. Bailey esti- 

 mated the Torridon at about 300 feet. This would make the base 

 of the series about 2600 feet above the sea, which agrees nearly 

 enough with my estimate of 2500 feet, taken by aneroid at a time 

 of considerable atmospheric disturbance. Judging by a large number 

 of blocks of red grit scattered over the gneiss slopes below the con- 

 glomerate, there can be no doubt that beds of this rock occur in the 

 precipices above. The grit and conglomerate are continued down 

 the Oykel valley for three or four miles ; but the thickness I found 

 not greatly to exceed 100 feet. 



The red variety is typically a quartzo-felspathic grit (Nos. 92, 

 93, p. 417). It occurs abundantly in the localities on the Oykel. 

 It is important to observe that these rocks are truly fragmental. 

 They are composed of material which might have been derived from 

 the Hebridean. 



In Ben More the conglomerate and grit rest in horizontal beds 

 upon the nearly vertical gneiss which forms the nucleus of the 

 mountain, and are overlain by the Ben-More quartzite, which I 

 regard as merely a faulted repetition of the quartzite under the 

 Dolomite. It would therefore appear that the grit represents the 

 Torridon sandstone. There are, indeed, slight differences, the Ben- 

 More grit being frequently green in colour, its particles being less 

 often rounded, and its general aspect more strongly suggesting deri- 

 vation from gneissic rocks. Whether ■ or not this group is exactly 

 contemporaneous with any part of the Torridon is immaterial. It 

 is sufficient for my purpose that it lies above the Hebridean and 

 below the quartzite. 



c 2 . Quartzite. — This series is tolerably homogeneous from top to 

 bottom ; but there are certain differences which render possible a 

 separation into two divisions, a lower (c 2 1.) and an upper (c 2 u.). 



Seamy Quartzite, c 2 l. — The base of the quartzite is characterized 

 by the occurrence of. thin seams of shale or grit and bits of red 

 felspar, and, in Assynt, by the intrusion of beds or masses of felsite 

 or diorite. The felspar grains are seen throughout Assynt at this 

 horizon ; and the seamy appearance is, so far as I have seen, per- 

 sistent along the whole line as far as the North Sea. Indeed the 

 uniform character of the quartzite is remarkable. About 10 feet 

 from the base is a thin seam of quartzose grit, which appears at the 

 same horizon at points over 30 miles distant on the strike. The 

 basemeut of the series in Assynt is often a thin band of conglo- 

 merate of quartz in a brownish matrix ; and a similar seam occupies 

 the same position on Loch Emboli. Towards Whitten Head the 

 partings expand, so as sometimes to reach a thickness of several feet. 



Annelidian Quartzite, c 2 u. {Pipe-rock). — The abundance of vertical 

 burrows has been noticed by most writers. I have been unable to 

 detect them in the lower series ; but they characterize the upper part 

 wherever I have studied the group — that is, from Loch Broom to 

 Loch More, a distance of 35 miles, and on Loch Emboli, 55 miles 



