1856.] NICOL — QUARTZITES, ETC. OF N.W. SCOTLAND. 21 



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limestone is of a bluish-white or grey colour, and intersected by so 

 many minute veins as to give it a brecciated structure. It is very 

 much hardened, and often siliceous. Interstratified with it are thin 

 beds of finely laminar shale ; the laminae are often as thin as paper, and 

 some of them light grey, others black and carbonaceous. The general 

 dip of the quartzite and limestone series of beds is about 15°-20° to 

 S. 60° E., thus at a higher angle and in a more easterly direction 

 than the red sandstone on which they rest. In the valley of the 

 river the limestone is followed by the same serpentine, or felspar- 

 porphyry rock, observed on Loch Broom, and this along Loch Auchal 

 by gneiss, dipping to the south-east. The immediate relations of the 

 rocks are, however, concealed by the lowness of the ground and the 

 thick cover of moss and grass. 



Any doubt on this point is removed by examining the hill between 

 Loch Auchal and Loch Broom, in the hue followed by the section. 

 The quartzite just described forms the first low acclivity, resting on 

 the red sandstone. Beyond a slight depression, the ground rises 

 more rapidly ; and, on the steep slope, first the limestone crops out, 

 then the serpentine, and above all the gneiss, forming the summit 

 of the hill, where it dips at 10°-15° S. 30° E., though with slight 

 undulations. The rocks may be traced round the south side of the 

 hill, placing their relations to each other beyond all doubt. A ver- 

 tical section through the summit would pass in succession through 

 the gneiss, serpentine, limestone, quartzite, and probably the red 

 sandstone. 



The section (fig. 2) on the south of Loch Broom is, if possible, 

 still more explicit. The western portion was only seen in sailing 

 along shore, as there is no road on this side of the loch, and the 

 cliffs are in many places inaccessible ; but the eastern, and most im- 

 portant part, was examined on the ground. At the north-west 

 extremity the red sandstone dips out to the sea, but is soon inter- 

 rupted by rocks represented as gneiss by Macculloch, and probably 

 the continuation of those subsequently noticed near Loch Greinord. 

 The red sandstone again commences dipping steadily to the south- 

 east, along the whole loch, to beyond Ullapool. From the Ferry, its 

 general dip is about 8° to S., 60° E., or S. 75° E., in thick, regular 

 beds. According to Macculloch' s map, the red sandstone is imme- 

 diately followed by gneiss ; but, as the section shows, this is not the 

 case. Before reaching Logic, it gives place to the quartzite, dipping 

 at 15°-20° to S., 70° E. Besides the common quartzite, I found both 

 the beds with cylindrical bodies, and those with fucoid impressions 

 observed on the north shore. I could not, however, discover the 

 hmestone, the quartzite being immediately succeeded by a thick mass 

 of the serpentine or porphyry, running as a bold overhanging cliff, 

 obUquely up the side of the hill, nearly in the dip of the beds. I 

 traced it from the shore to the top of the ridge, and it apparently 

 extends round into the valley at the head of Little Loch Broom, 

 forming the cliffs beyond Dundonald. From its great hardness, it 

 projects in a broad ledge or terrace, but is covered by gneiss, 

 dipping at 23° nearly due east ; and, like that on the north shore. 



