part 2] THE SOUTH-WEST HIGHLAISTDS OF SCOTLAND. 113 



rock-belts ushered in by the quartzite just mentioned present 

 themselves in the following order : — 



(1) Quartzite, forming- a continuous belt wMch. is easily traced, about 

 100 yards broad in its northern exposures, and 500 yards broad, where, in 

 Garbh Ard, it finally goes out to sea. It is essentially fine-grained (in fact, 

 pebbles are very rare indeed), thinly bedded, and white. 



(2) Greenish-grey Phyllite with dark seams. In the north the outcrop is 

 600 yards wide, but is interrupted by four or five bands of quartzite, 

 with sufiiciently broad outcrops to be shown on a 6-inch map ; they are 

 probably folded repetitions of (1). Southwards the phyllite outcrop is un- 

 broken, and is only 100 or 200 yards wide. A good exposure is afforded on 

 the northern shore of Loch Creran, and another in a ridge, a little south of this 

 loch, at Baracaldine Castle. The phyllite is last seen succeeding the Garbh- 

 Ard Quartzite (1) south-west of Lochan Dubh. 



(3) Black Slates followed by a mixed assemblage of Black Slate, Quartzite, 

 and subordinate Limestone. 



The succession grouped under (3) can be studied in shore- 

 sections on the north side of Loch Creran (3«), or south of the 

 loch eastwards from Rudha Glarbh (3 5), or, again, at Selma on 

 Ardmucknish Bay (3 c) : — 



(3 a) North of Loch Creran, jet-black graphitic slates, rich in pyrites, give 

 place south-eastwards to black slates varied by the incoming of quartzite- 

 bands, some of them pebbly ; but, for about 1000 yards, these quartzite inter- 

 calations are quite subordinate. Then follows a belt of predominant 

 quartzite, forming a fairly prominent ridge. Where examined, the quartzite 

 of the ridge proved to be well bedded and associated with thin partings of 

 black slate. Pebbles were noted in some of its bands. Perhaps this quartzite 

 has a discontinuous outcrop pitching up into the air without actually 

 reaching the shore ; but the exposures leave this in doubt. Beyond a gap 

 in the coast-section (which appears to correspond to black slate with occa- 

 sional pebbly beds seen a little inland) fairly definite quartzite is once again 

 encountered, constituting the headland at the turn of the loch and also the 

 north-eastward trending coast for a mile beyond. The quartzite in these 

 excellent shore-exposures carries intercalations of dark and black slates, as 

 well as of more or less sandy, pale-grey, dark-grey, and black limestones. All 

 three rock-types (quartzite, slate, and limestone) are often seen to be pebbly 

 with large grains of blue and white quartz and felspar, and one of the 

 limestone-beds carries in addition small pellets of penecontemporaneous 

 sediment. 



(3 h) The exposures south of the loch, east from Eudha Garbh, are too 

 similar to those just described on the opposite shore to deserve detailed 

 description. At Eudha Garbh, black slate predominates, pyritous as usual, 

 and associated with subordinate quartzite and black limestone. This belt is 

 followed eastwards by a succession of outcrops in which the mastery lies 

 sometimes with quartzite, sometimes with black slate ; while dark limestone 

 is in either case a subordinate, though characteristic, associate. The qixartzite 

 is generally fine in texture, but occasionally pebbly with grains of blue and 

 white quartz and also felspar ; and some of the dark slaty bands carry 

 similar pebbles. This alternation continues until slaty-grey phyllite takes it& 

 place about 100 yards west of a fault introducing lavas of OldKed Sandstone 

 age into the shore-section. 



(3 c) The Selma exposures on Ardmucknish Bay recall those of Rudha 

 Garbh, with its black slate, limestone, and quartzose beds ; the section is 

 chiefly noteworthy for a cleaved breccia, which Dr. J. S. Flett has given good 

 reason to believe may be a crush-conglomerate (1908 &, p. 58). 



Q. J. a. S. No. 310. I 



