﻿1861.] 



MTTRCHISON AND GEIK.IE HIGHLANDS, 



183 



came one thick limestone resting on quartz-rock, and dipping below 

 gneissose flaggy beds. This limestone follows a curved, sinuous 

 line across the hilly ground to Loch Auchall, now seeming to dis- 

 appear beneath the vegetation, and then swelling out again into 

 irregular lenticular mounds and ridges. The curving of the line 

 of strike conforming in great measure to the contour of the ground, 

 shows clearly enough that there is no great line of fault here. The 

 strata dip to the south-east, and unequivocally pass under a superior 

 group of thin-bedded micaceous and quartzose schists. 



Before quitting Strath-Kennort, it may be well to mention that 

 this deep valley affords a good illustration of the varieties of form 

 and colour imparted to a landscape by changes in the character 

 of its composing rocks. Standing at the lower opening of tbe strath, 

 all is sombre and brown. The dull-red Cambrian sandstones, hoary 

 with lichens, project their rounded edges out of a shaggy mantle 

 of dun heather and stunted bent. Further up the glen, however, 

 where the quartz-rock descends upon the slopes, masses of snowy 

 crag stand out from the dull herbage. Beyond this a bright-green 

 knoll, protruding from the brown hillside into the browner valley, 

 reveals the presence of the limestone, while, far away at the head of 

 the strath, dark crags and grey scars, rising terrace over terrace, 

 with still the same dull heath between and above them, show where 

 the upper gneissose beds have begun to set in. 



Loch Auchall. — The sections in the deep gorge of the Auchall, 

 from the lake to the sea near Ullapool, afford a clear exposition of 

 the order of succession. They have been well described by Pro- 

 fessor Mcol*; and we cannot resist quoting a passage from his 

 memoir. " On the steep slope," he says, " 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 vertical section through the summit would pass in suc- 

 cession through the gneiss, serpentine, limestone, quartzite, and 

 probably the red sandstone." 



The limestone in this section has attained a great thickness. We 

 estimated it at somewhere about 500 or 600 feet. The " serpen- 

 tine " of Professor Nieol deserves some notice. In his section of 

 Loch Broom he has represented this rock as a bed intercalated be- 

 tween the limestone and his " upper gneiss." And this is un- 

 doubtedly its true position, although he has subsequently endea- 

 voured to explain away what he at first regarded as " beyond all 

 doubt," by supposing that the " serpentine " has come up in a great 

 line of fissure, and that the " upper gneiss " is not upper gneiss at 

 all, but the old Laurentian rock brought up by a gigantic fault. 



The rock, as seen at Loch Auchall, we should call a porphyry, or 

 porphyrinic felstone with serpentine. It is disposed in rude beds, 

 irnder which the limestone dips, and which are ranged in parallel 

 ridges dipping in the same direction with the limestone. Near the 

 * Quart. Journ. Greol. Soc. vol. xiii. p. 21. 



o2 



