IN THE NOKTH-WEST HIGHLANDS OF SCOTLAND. 419 



Thrust-plane. For several miles of its course, from a point near 

 Loch na Gainmhich to Cnoc an Droighinn, this maximum thrust 

 brings various members of the quartzites to overlie different sub- 

 divisions of the Ghrudaidh and Eilean Dubh limestones. These 

 quartzites have been driven westwards with the great slice of 

 Archaean rocks above this thrust-plane, the latter rocks being ex- 

 posed, with their characteristic basic dykes, to the north of the 

 Chalda Lochs. But it ought to be borne in mind that the quartz- 

 ites along the western face of the disrupted gneiss do not lie in 

 regular inverted order : they are traversed hj numerous thrusts, 

 bringing different subdivisions of the quartzites with their intrusive 

 sheets against each other. The extreme complications resulting 

 from these minor thrusts and subsequent folding in the quartzites 

 and their associated igneous rocks are splendidly displayed in 

 Cnoc an Droighinn near Inchnadamff. 



Between Glasven and Ben Uidhe there is a powerful maximum 

 thrust driving westwards the Archaean gneiss with the basal quart- 

 zites and the " pipe-rock," while on the crest of the latter mountain 

 both zones of the quartzites are repeated by various thrusts. On 

 the northern shoulder of MuUach an Leathaid Riabhaich several 

 powerful thrusts and extraordinary flexures of the strata are met 

 with, until we reach the horizon of the Ben-More Thrust-plane, at 

 the head of Glenbeg. 



The Limestone Plateau at Inchnadamff. — The great development 

 of Silurian limestone at Inchnadamff occurs almost wholly within 

 the area ajffected by the Post-Lower- Silurian movements. Indeed it 

 is rather remarkable that only one small patch, belonging to the lower 

 subdivision of the Ghrudaidh group, lies in the undisturbed area, viz. 

 on the north shore of Loch Assynt near the mouth of the Skiag burn. 

 Between Achumore and Inchnadamff the belt of limestone is nearly a 

 mile wide, but to the east of the great Stronechrubie cliff it forms a 

 broad plateau about two and a half miles in width. As indicated in 

 the foregoing vertical Section II. (p. 406), the beds belong mainly to 

 the two lowest groups of the Durness limestones, only a small portion 

 of the Sailmhor group being represented. Owing to the extraordinary 

 complications of the strata, due to the number of minor and major 

 thrusts, it is difficult to estimate accurately the thickness of the lime- 

 stones, but it cannot exceed 450 ft. or 500 ft. 



That the calcareous beds are not arranged in an inverted synclinal 

 fold can be demonstrated in the most conclusive manner. Taking 

 first that portion of the plateau between Inchnadamft' and Achumore, 

 the following horizontal section (fig. 14) shows the general relations 

 of the strata. Starting from the shore of Loch Assynt, about half a 

 mile north of the mouth of the Traligill, the "Fucoid-beds," Serpulite- 

 grit, and a portion of the basal limestones are repeated by numerous 

 minor thrusts, till we reach a powerful major thrust-plane, along 

 which the Eilean Dubh limestones have been driven westwards, 

 over the underlying Ghrudaidh Group. Within a distance of half 

 a mile of the shores of the Loch, the piled up limestones are trun- 

 cated by another major thrust, bringing up the " Fucoid-beds," Ser- 

 pulite-grit, and basal limestones to overlie the Eilean Dubh beds. 



