480 MR. J. B. HILL ON PEOGEESSIVE METAMOEPHISM [Aug. 1899, 



Y. Evidence of Peogeessive Metamoephism. 



The mapping of the district has shown that the different zones 

 between Loch Fyne and Loch Awe have a steady north-easterly 

 strike. Not only has the series as a whole a steady strike, but the 

 different beds which are contained in them pursue a more or less 

 even course in a north-easterly direction. As the beds are 

 continued past the upper reaches of Loch Fyne, we have, for the 

 first time for many miles, a change in the persistent north-easterly 

 strike. The Ardrishaig and the Loch Awe Series are here arranged 

 in a series of compound folds, by means of which the outcrops are 

 curved backwards and deflected for several miles to the west of the 

 general line of outcrop. By this means the beds of the Ardrishaig 

 Series, hitherto occupying more or less the horizon of Loch Fyne, 

 have been curved round to the westward until they not only reach 

 Loch Awe, but make up the island of Inishail and small islets in its 

 vicinity, at the mouth of the Pass of Brander, and extend for about 

 2 miles on the west side of Loch Awe before they loop round, 

 and continue a more or less easterly direction past Dalmally, 

 until they reach the western flanks of Beinn Laoigh, when they 

 pursue their normal north-easterly direction. The lower members 

 of the Loch Awe Series, of course, follow round the fold in 

 conformity with the Ardrishaig Series that lies below them. It 

 is in this big loop formed by the fold that the progressive meta- 

 morphism is best seen. The beds occurring in the extreme end 

 of the loop on the west side of Loch Awe are comparatively 

 unaltered. The same beds, continued to the north, north-east, 

 and east, eventually pass within the space of a few miles into 

 coarsely crystalline granulitic rocks. The rocks in their least 

 altered forms can be best seen in that part of Lome, on the west 

 side of the Pass of Brander, that lies between Kilchrenan to 

 the south, and Tervin on the Pass of Brander to the north. The 

 beds are very much folded, with dips of folds at various angles ; 

 yet the series as a whole is nearly horizontal, so that one 

 particular zone of the seiies may occupy a large area. From 

 Kilchrenan to Ben Laoigh, in an easterly direction, the change is 

 gradual. Proceeding from the Kilchrenan district northward to the 

 Pass of Brander, the change is sudden and rapid. In this instance, 

 however, we are approaching directly the great mass of the Cruachan 

 granite, and much of the alteration can with certainty be assigned 

 to contact-metamorphism produced by this granite. I will describe 

 first the alterations produced in the Ardrishaig phyllites as they are 

 traced from west to east. 



In its least altered state the Ardrishaig Series is well seen on the 

 coast at New Inverawe, the southern entrance of the Pass of Brander. 

 Here grey and greyish-green phyllites occur, lying nearly flat, the 

 strata sometimes rolling. They are made up of thin alternations 

 of phyllite and limestone, the phyllite preponderating. In places 

 the phyllites are very little removed in condition from clay-slates. 

 They split along cleav9ge-planes, and show a lustrous surface on those 



