96 ME. E. B. BAILEY OX THE STEUCTUEE OF [vol. Ixxviii, 



the reader is asked to excuse a rather dogmatic statement of the 

 case. 



The outcrop of the nappe reaches south-westwards from the 

 northern end of Loch Awe, until lost sight of under the sea. 

 Its breadth is roughly 20 miles, and its position is clearly 

 indicated in PL I. The stratigraphical succession within its 

 limits is as follows : — 



Loch.- Awe 

 Group. 



"Loch Avicli, green Slates with grits, and (in the basal 



part) pillow-lavas. 

 Tayvallich, black Slates and limestones (both often 



pebbly), grits, conglomerates, and pillow-lavas. 



(Pebbly -<j The rock-fragments in the conglomerates are generally of 



local origin ; but, in certain well-known occurrences, nord- 

 markite and other foreign boulders are found. 

 Crinan Grits and Quartzites with subordmate slates 

 and limestones. 

 )-Shira Limestone, grey or cream-coloured, according to 

 locality ; absent south of the Crinan Canal, and, elsewhere, 

 often interbedded with greenish-grey phylhtes. 

 Ardrishaig, soft, greenish-grey Phyllites, with cal- 



character 

 recurrent.) 



Ardrishaig 



Group. 



(Pebbly cha- <j careous lenticles, occasional beds of buff-coloured or white 



racter very hmestone, and a fair proportion of compact, fine-grained, 



restricted.) slightly-calcareous quartzite. 



i Erins fine-grained, shghtly calcareous Quartzite, restricted 



1^ to Lower Loch Pyne. 



Basic sills (epidiorite) are abundant everywhere, except in the central 

 portion of the outcrop of the Loch-Avich Slates. 



The separation of the Loch- Awe and Ardrishaig Grroups is due 

 to Mr. J. B. Hill (1899, p. 473). The subdivision of the Loch- 

 Awe Group (1913 h, p. 291) followed closely on Dr. B. X. Peach's 

 recognition of volcanic rocks in the Tayvallich Peninsula (190-4 h, 

 p. 68 j.^ The Erins Quartzite was early distinguished by Mr. Hill : 

 he regarded it as a local facies of the lower part of the Ardrishaig 

 Group. 1 am inclined to think that it is a separate entity, and 

 that it owes its restricted occurrence to limitation by the thrust at 

 the base of the Loch- Awe Nappe. 



At one time, I imagined (1913 h, p. 300 & pi. xxxii) that the 

 Erins Quartzite probably belonged, half to the Ardrishaig Group, 

 and half to the Ben-Lui Group (p. 95). This working hypo- 

 thesis was based upon a couple of rather insecure foundations : — 



(1) A tentative correlation, connecting certain graphitic phyllites at Stron- 

 chullin, in the heart of the Erins Quartzite, south of Ardrishaig, with similar 

 rocks occurring in bands at the north-western margin of the Ben-Lui Group, 

 18 miles farther up Loch Eyne. 



(2) A tacit assumption that the StronchuUin outcrop does not mark the 

 centre of a fold. 



Now that other evidence points to a complete structural 

 separation of the Ardrishaig Phyllites (Loch-Awe Nappe) from 

 the Ben-Lui Schists (Iltay Nappe), partition of the Erins Quartzite 

 is no longer possible. 



^ See also 1922, Eeport A, par. 1. 



