12-i ME. E. B. BAILEY OX THE STRUCTUEE OF [vol. IxxVlii, 



It will be readily understood that a small district does not afford 

 opportunities for establishing a big structure. Accordingly, in 

 reading this description, constant reference must be made from 

 fig. 8 to PL I. 



In the first place, although the superposition of Ben-Lawers 

 Schists on Ben-Lui Schists in the upper limb of the Ben-Lui Fold 

 is quite obvious in the immediate neighbourhood of Ben Lui, 

 there is no local evidence to show that this order of superj^osition 

 is of Avide extent. To realize the importance of the upper limb of 

 the Ben-Lui Fold, one has to remember the clear evidence from 

 Loch Tay to Campbelton of the superposition of the Ben-Lui 

 Schists on Loch-Tay Limestone — a superposition which continues 

 for about 15 miles across the strike (p. 103). In this matter I 

 have merely confirmed the findings of my predecessors. 



Again, the superposition of Ben-Lui Schists on Ben-Lawers 

 Schists in the lower limb of the Ben-Lui Fold is quite an obvious 

 feature of the geology of the northern face of Ben Lui. The 

 reality of the downward succession is enforced on anyone who 

 descends the tectonic ladder connecting Ben Lui with Ben 

 L'dlaidh, where the Sub-Eilde Complex is so definitely exposed. 

 The extent of country throus^h which the lower limb of the Ben- 

 Lui Fold has been traced will escape no one who recollects how 

 Easdale Slates overlying Islay Quartzite have been followed from 

 Ben Lui westwards round the outcrop of the Ardrishaig Phyllites 

 into the Islay Archipelago. 



Prof. Collet several times complained that grassy slopes compeEed Mm to use 

 his legs as well as his eyes to realize this fact. It may be helpful to record 

 some important features recognized during our joint traverse : — 



(1) Ardrishaig Phyllites form a prominent escarpment, Ra Chreag, where 

 they overlie the Easdale Slates of the upper limb of the Ben-Lui Fold west 

 of Allt Coire Lair (for place-names, see 1-inch map, Sheet 45). 



(2) The junction of the Ardrishaig Phyllites and Easdale Slates can be 

 located to within a foot or so at the base of E.a Chreag, in a stream which, at 

 the valley-bottom, passes Corryghoil. 



(3) The Easdale Slates below Ea Chreag are marked scenically by a grassy 

 slope, where exposures are almost restricted to stream-courses. 



(4) The Ben-Lawers Schists immediately below the Easdale Slates crop 

 out as a subdued escarpment. 



(5) Although the easternmost stream-exposure of the Easdale Slates is 

 afforded by Allt Coire Lair, the Ardrishaig and Ben-Lawers escarpments are 

 distinguishable for some distance farther. Li Meall nan Gabhar the Ardri- 

 shaig escarpment seems to overreach its comi:)anion and come into direct 

 contact with Ben-Lui Schists. 



(6) The appearance of Meall nan Gabhar is very suggestive of a thrust- 

 mass, riding upon a thrust-plane at the base of the Ardrishaig Phyllites. 

 The features of Meall nan Gabhar almost certainly indicate that the bedding 

 within the Ardrishaig Phyllites is much more steeply inclined south- south- 

 westwards than is the base of the Ardrishaig escarpment. Probably the 

 high dip is due to some sj)ecies of schuppenstruktur, audits direction, 

 as Mr. Eichey pointed out to me, lends support to the view that the Loch- 

 Awe Nappe has travelled in a general south-eastward direction. From this 

 interpretation, it would follow that some of the many minor complications of 

 the Loch- Awe Nappe belong, as might be expected, to the primary category 

 of movements. — E. B. B., January 1922.1 



