Vol. 55.] PROGEESSIVE METAMORPHISM IN LOCH AWE DISTRICT. 473 



schistose grits and limestones, with a breadth of about 1| mile ; next, 

 a series of chlorite-epidote schists, generally pebbly. North- west 

 there is a zone, 7 miles broad, of schistose grauwackes, phyllites 

 and albite-schists. This is the zone where, as we approch an anti- 

 clinal axis of foliation, an increasing amount of metamorphism is 

 met with, decreasing again as we recede from this axis in a north- 

 westerly direction. After this wide zone we find another set of 

 chlorite-epidote schists. This zone is succeeded by the Loch Tay 

 Limestone, which is the most definite of all the sedimentary schists 

 of the district. After this w^e get a series of thin banded mica- 

 schists, generally garnetiferous. Finally we find, as we approach 

 Loch Fyne, the broad Ardrishaig Phyllite Series with subordinate 

 quartzose schists and limestones. 



The Ardrishaig phyllites and the beds which succeed them to the 

 north-west are described in this paper, but it is not proposed to 

 enter into a description of the foldings and structures set up in 

 them, as this would be largely a repetition of what has been already 

 fully discussed in dealing with the south-eastern extension of the 

 district in Cowal. 



III. Description of the Ardrishaig Series and the 

 Loch Aw^e Series. 



The two great groups of rocks entering into the structure of the 

 region now to be described are : — 



(1) The Ardrishaig Series (consisting mainly of phjdlites 

 and fine-grained quartzites) and 



(2) The Loch Awe Series (consisting mainly of black 

 slates, limestones, grits, and quartzites). 



The Ardrishaig Series occupies a strip of country on both sides of 

 Loch Fyne. From Ardrishaig the series extends north-eastward 

 along Loch Fyne, passing Inveraray, Beinn Buidhe, and sweeping 

 past the western flank of Beinn Laoigh into Perthshire. 



The Loch Awe Series occupies a position immediately to the 

 north-west of the Ardrishaig Series. It occurs mainly in the Loch 

 Awe basin, and follows the north-easterly strike of the Ardrishaig 

 Series lying to the south-east. 



The evidence of progressive metamorphism is obtained as the 

 observer passes north-eastward. 



I will first of all notice the lithological characters of the rocks in 

 their least altered form ; and afterwards, the changes that they 

 have undergone in their passage into crystalline schists. 



The Ardrishaig Series, where least altered, consists of: — 



(a) Greenish phyllites, very soft, scratching easily with the nail ; 



(6) Fine-grained greyish quartzite ; and 



(c) Thin limestones, greyish to white, weathering rusty brown. 



They are typically illustrated at Ardrishaig, where they were 

 first mapped, hence their name. A more detailed description of 

 them will be found in the Survey memoir previously quoted. 



