﻿102 



PROCEEDINGS OE THE GEOLOGICAL SOCIETY. 



[Dec. 5, 



to the surface, followed (still to the east) by fine-grained gneiss, 

 much curved and contorted, but dipping at 35° to 50°, to S. 5° "W. 

 In this line a thin vein of granite or syenite, like that on Loch Em- 

 boli, intervenes. Further south, on the Ullapool road, the line of 

 junction intersects the front of the vertical cliff, and the strata are 

 well exposed. The quartzite, dipping at 5° or 6°, and covered by 

 the fucoid-beds and limestone, comes within a few yards of the gneiss. 

 A thick, strong bed of the quartzite then dips down at 12°, as if 

 below the gneiss, whilst the thinner fucoid-beds above are curved 

 and fractured and the limestone broken suddenly off. The dark- 

 coloured, thin-bedded gneiss dips at 20°, and is traversed by innu- 

 merable fissures, filled with thin lines of the granitic rock, running 

 up the face of the cliff, from which, a little to the south, a large 

 mass of trap protrudes. Had the strata been less clearly exposed, 

 the gneiss might have been supposed to overlie the quartzite ; but 

 the fracture and contortion of the beds, seen even in hand-specimens, 

 and particularly the manner in which the limestone and fucoid-beds 

 are cut out, prove that there is, in this place, not " conformable 

 upward succession," but a line of fault with powerful lateral com- 

 pression. 



Loch Broom. — The next point to the south where the rocks are 

 well seen is the vicinity of Loch Broom, described in my former 

 paper*. As there stated, the quartzite is cut off from the gneiss by 

 a thick bed of intrusive rock, in some places a felspar-porphyry, in 

 others near the limestone inclining to serpentine, but generally 

 identical in character with the rocks in the same position in the 

 previous sections. This summer (1860) I again visited Loch Broom, 

 but saw little to add to my former memoir, except that the porphyry 

 or igneous rock is more extensive than represented in the sections, 

 and, rising up in a wider mass below, separates the eastern gneiss 

 more strongly from the quartzite. I must also call attention to the 

 fact, exhibited in the sections, that, whilst on the north shore the 

 series of the quartzite group is complete, on the south side of Loch 

 Broom the limestone above has been entirely cut out. 



Loch Maree and Gairloch. — In my former paper I described some 

 sections in the vicinity of the Gairloch and Loch Maree. I have 

 since examined the mountains round the upper portion of that most 

 beautiful lake, and the line of junction between the quartzite and 

 gneiss with some care; and the section (fig. 11, p. 104) shows the facts 

 as seen on the north side of the loch. In the west there is, first, the 

 red sandstone (6), dipping west at a low angle, as seen near Pol Ewe 

 and the Gairloch. Then follows the gneiss, as formerly stated, often 

 a fine-grained grey rock with intercalated beds of mica-slate, in Ben 

 Lair, with hornblende-strata. Near the head of the loch the red 

 sandstone cone of Sleugach rises above a basis of gneiss, forming one 

 of the grandest mountains in this truly mountain-region. The 

 gneiss, generally red or grey and highly crystalline, where seen 

 below the red sandstone dipped 70°-80°, toW. 20° S., and hence has 



* Quart. Journ. Geol. Soc. vol. xiii. (1856) p. 18-24 and figs. 1 & 2. 



