IN THE NORTH-WEST HIGHLANDS OF SCOTLAND. 



417 



As the observer passes southwards to 

 Gleudhu and Glencoul (fig. 11), the out- 

 crop of the Gleucoul Thrust-plane is mag- 

 niticentl)^ displayed in dip-section in these 

 sea lochs. To the west lies the natural 

 escarpment of the basal quartzites and 

 ** pipe-rock," resting unconformably on 

 the undisturbed Archaean platform ; and 

 within a distance of half a mile to the 

 east occurs an enormous slice of the 

 old crystalline rocks, which has travelled 

 for miles along the '' sole " of the Glen- 

 coul Thrust. Underneath this maximum 

 thrust, however, there is a powerful major 

 thrust driving forward the "Fucoid- 

 beds," Serpulite-grit,and basal limestone 

 piled up by numerous reversed faults, 

 the latter being admirabl}- seen in dip- 

 section in Loch Glencoul. 



The great mass of Archaean rocks 

 brought forward by this maximum 

 thrust rises from the sea-level like a 

 wall round the head of Loch Beag, to 

 a height of over 1750 feet, presenting 

 the typical features of the Archaean 

 gneiss to the west with the basic dykes. 

 Ascending the ridge of Archaean rocks 

 on the south side of the Glen to the 

 Stack of Glencoul, various Silurian zones 

 dip towards the E.S.E., piled on each 

 other by minor thrusts. A careful exa- 

 mination of the sections shows that 

 these zones are separated from the 

 Archaean rocks by a powerful thrust- 

 plane which descends the slope at a high 

 angle. There can be no doubt what- 

 ever that these Silurian zones have been 

 driven westwards along the " sole " of 

 this thrust. 



At the base of the Stack of Glencoul 

 the Silurian quartzites have undergone 

 important changes, due to the move- 

 ments which will be refered to presently. 

 They are overlain by a thin belt of green 

 schist, the latter being rapidly succeeded 

 by the micaceous flagstones above the 

 Moine Thrust-plane. 



Advancing south-eastwards towards 

 Cnoc an Fliuarain Bhain (^fig. 12), across 

 an area of intense complication, all the 





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