426 



EECENT WOEK OF THE GEOLOGICAL SURVEY 





^ 



heart of the latter displaced materials a small 

 patch of Archsean rocks has been exposed by 

 the denudation of the basal quartzites. In ad- 

 dition to the latter, all the Silurian zones, up to 

 the horizon of the Eilean Dubh limestones, have 

 been borne westwards along this disruption- 

 plane, comparatively unaltered in places, till we 

 approach the micaceous flagstones above the 

 Moine Thrust-plane, where the quartzites have 

 been converted into quartz-schists, and the dykes 

 have also been rendered schistose. 



Advancing southwards to the Knockan clifi^, 

 about two miles to the south of the foregoing line 

 of section, there is a remarkable difference in 

 the order of succession of the strata. 



On the eastern slope of Coul More the basal 

 quartzites rest unconformably on the Cambrian 

 sandstones, followed in natural order by the 

 "pipe-rock," " Pucoid-beds," and Serpulite-grit, 

 the latter being exposed on the Knockan cliff 

 east of Lochan Fasaig. Overlying the Serpulite- 

 grit in natural sequence, there is a small portion 

 of the basal limestone of the Ghrudaidh group, 

 which is abruptly truncated by a major thrust- 

 plane, bringing forward the white limestones and 

 marble of the Eilean Dubh group. The latter 

 are succeeded by the finely laminated micaceous 

 flagstones above the Moine Thrust-plane. 



Following the outcrop of this thrust-plane 

 southwards to Strath Kanaird, a distance of 

 nearly six miles, the Moine micaceous flagstones 

 rest, now on the basal limestones, now on the 

 Serpulite-grit, and again on the " Fucoid-beds," 

 passing transgressively from one horizon to the 

 other, thus showing the complete discordance 

 between the materials above and below the 

 thrust-plane (fig. 20). As the flagstones lie on 

 the undisturbed beds, there seems at first sight to 

 be a natural passage from the Silurian strata into 

 the eastern schists ; but the apparent conformity 

 is entirely deceptive. 



That such is the true explanation of the rela- 

 tions of the strata along this line of section is 

 still further confirmed by the remarkable evi- 

 dence in Strath Kanaird, near Langwell. About 

 a mile to the east of the normal outcrop of the 

 Moine Thrust, the river has cut down through the 

 thin cahe of micaceous flagstones^ and exposed 

 on the south side of the valley a large mass of 

 Archcmn gneiss, covered unconformcibly hy the 



