Vol.69.] loch awe syncline (Argyllshire). 301 



band of epidiorite from typical grey and green pbyllites ; on the 

 west it is followed almost directly by massive beds of fine-grained 

 grit with, at first, intercalations of grey- green pbyllites of Ardri- 

 sbaig type. When the phyllitic beds cease the fine-grained grits 

 are so massive that their bedding is not easily discerned. There is 

 no doubt at all that these grits, or fine-grained pebbly quartzites, 

 belong to the Crinan Division. 



I have seen very little of the junction-line between the Ardri- 

 shaig and Loch Awe Groups, from this point north-eastwards to the 

 wide outcrop of limestone shown on the map (PI. XXXII) 15 miles 

 north-east of Ardrishaig. Here a visit made it obvious that an 

 important limestone separates the Ardrishaig Phyllites from the 

 Crinan Quartzite. It has the same characters as in Glen Shira — 

 the type-locality with which I shall deal in detail presently. 



Again, until Glen Aray is reached, I have no personal know- 

 ledge of the Shira Limestone. In Glen Aray that rock is involved 

 in a porphyry intrusion, but its original characters are not de- 

 stroyed. It consists of a thick mass of limestone weathering to 

 a cream colour, with pale-grey . fracture, and is much split up by 

 partings of pale-grey phyllite. Xorth-west of the porphyry is 

 alluvium ; but the first rock seen in the valley-bottom is massive 

 somewhat pebbly quartzite, associated with a thin band of cream- 

 coloured limestone. 



Capital exposures are afforded by the tributary burns draining 

 from the west into Glen Shira. The .second burn south of Drimlee, 

 5 miles north-east of Inveraray, may be cited as typical. The 

 greater part of this magnificent section, as one ascends from the 

 Shira, is occupied by greenish-grey silvery phyllites. At first, a 

 homogeneous mass of these phyllites is encountered, scarcely 

 interrupted except by igneous rocks : fully three-quarters of the 

 section is of this type. A change is ushered in by the appearance 

 of several well-marked, fine-grained quartzite-bands. Above this, 

 beds, ribbons, and lenticles of cream-weathering sandy limestone, 

 grey and cream-coloured on the fractured face, are continually 

 appearing intercalated in the phyllites. Where numerous, they give 

 added power of resistance to the whole, and the stream rushes 

 across their outcrop in a series of picturesque cascades. The pro- 

 portion of limestone to phyllite is, as a rule, not very high ; but, 

 looking down upon the exposed dip-slopes above these waterfalls, 

 the cream-coloured backs of the limestone-beds make a very con- 

 spicuous feature. This type of sedimentation prevails right up to 

 the base of the Crinan Quartzite, save that strong beds of grey 

 sandy limestone, intercalated with grey phyllite, occur in contact 

 with the quartzite. In these dark limestones one has a foretaste of 

 the carbonaceous character so prevalent in the Loch Awe Group. 

 In the sections which remain to be described, the Shira Limestone 

 exhibits this character much more strongly ; and it" is on this 

 account that the division is regarded as transitional between the 

 Ardrishaig and the Loch Awe Groups. 



I have not followed the Shira Limestone continuously in it* 



