part 2] THE SOUTH-WEST HIGHLANDS OP SCOTLAIID. 99 



Transition Group, including- Black Slates and Quartzites. Con- 

 glomerates occur in Scarba, Jura, and Islay, and grey pliyllite 

 (Port Ellen Phyllites) in Southern Jura and Islay. There are 

 also limestone-bands, sometimes pebbly. 



Islay Quartzite in part pebbly, especially towards the margin of the 

 Transition Group : locally, a flaggy dolomitic group occurs within the 

 quartzite not far from the Portaskaig Conglomerate (Northern Islay) ; 

 locally also, a flaggy semipelitic pebbly group develops not far from 

 the Transition Group (Northern Jura, Scarba, etc.). 



Portaskaig Conglomerate, with nordmarkite and other boulders. 



Islay dark-grey Limestone, locally oolitic; this limestone and the 

 MuU-of-Oa Phyllites are to some extent interbedded. 



Mull-of-Oa grey or greenish Phyllites with dark colour-striping ; 

 thin cream-coloured sandy dolomites are common in some exposures. 



Maol-an-Phithich fine-grained Quartzite. 



It must not be thought that the succession outlined here is to 

 be met with as a whole in any one locality in the South- West 

 Highlands. The constitution of the Iltay Nappe varies notably 

 from place to place, according to the positions of the thrust-planes 

 which serve as its boundaries above and below. The variation can 

 be summarized as follows (see PI. I) : — 



District. ! Partial Succession. 



(a) Islay Archipelago, north-west of 



the Loch-Awe Nappe. 



(b) Kintyre and Cowal, soixth-east of 



the Loch-Awe Nappe. 



(c) Strip connecting (a) and (b) round 



the northern end of the Loch- 

 Awe Nappe. 



(d) North-eastward continuation of 



(&) and (c) towards Loch Tay. 



Maol-an-Fhithich Quartzite to Eas- 



dale Slates. 

 Ben-Lawers Schists to Leny Grits 



(with a concealed underground 



continuation of the rocks of the 



Islay Archipelago). 

 Islay Quartzite to Easdale Slates. 



Islay Quartzite to Leny Grits. 



The detailed evidence upon which I base my reading of the 

 stratigraphy of the Islay Archipelago («) has been recently 

 explained in the Quarterly Journal of this Society (1917). 

 It must be admitted, however, that Dr. Peach and Mr. Wilkinson 

 previously put forward an interpretation differing in various im- 

 portant particulars (1907 a). The statement of the Kintyre, Cowal, 

 and Loch-Tay sequence (5 & d) represents the verdict of my prede- 

 cessors — Clough, Cunningham-Craig, Macnair, Hill, Kynaston, and 

 Grrant Wilson. The three last-named are more especially responsible 

 for tracing that part of the succession which extends through the 

 Calcareous Schist (Ben-Lawers G-roup) into the Black Schist and 

 Pebbl}'' Quartzite cropping out farther north. The geology of the 

 intermediate belt (c), complicated as it is by granitic intrusion, 

 has not been adequately described as yet, and will according!}^ be 

 dealt with later on (p. 117).^ 



It will be readily understood, after what has just been stated, 

 that definitely synthetic treatment is requisite to realize the full 



^ See also 1922, Report A, par. 8. 



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