T^ol. 55."] IN THE EEGION OF LOCH AWE. 489 



as confirmatory evidence in support of the contention that the 

 deposits in which they occur are contemporaneous over the whole 

 region. 



It has been shown that highly crystalline schists of the Central 

 Highlands have been traced along their strike into beds of various 

 -degrees of metamorphism, which at last is so feeble in character 

 that the schistose structure becomes ever less apparent, in parts 

 dying out altogether. In the division known as the Ardrishaig 

 Series the nature of the ground has been such that I have been 

 able to join up the beds, step by step, without a break,; along 

 the strike, from the condition of highly crystalline schists to beds 

 hardly more altered than the Silurian rocks of the South of 

 Scotland. The evidence of this progressive metamorphism in the 

 Ardrishaig Series is so conclusive that the object of this paper would 

 have been attained without describing similar phenomena in the 

 Loch Awe Series, which normally succeeds it. But it has been 

 also shown that on similar horizons the crj'stalHzation of the Loch 

 Awe Series conforms to that of the Ardrishaig Series, which lies 

 next to it. Whenever the degree of metamorphism begins to 

 vary in one series, a similar change is observed in the adjoining 

 series. Owing to the nature of the ground and the presence of the 

 great sheet of water of Loch Awe, the uninterrupted line of in- 

 creasing metamorphism along the strike of this series cannot be 

 continuously traced, except in the neighbourhood of the Cruachan 

 granite, where the presence of this mass is responsible for much of 

 the alteration and hornfelsing that come on so suddenly in the Pass 

 of Brand er. But although this granite has effected great contact- 

 metamorphism where its southern margin abuts against these Loch 

 Awe sediments, yet where they are traced in a north-easterly direction 

 in their passage across the Central Highlands they do not revert to 

 their former unaltered condition, even when followed far away from 

 the granite. Their tendency, on the other hand, is rather to increase 

 still further in crystallization. It is, therefore, evident that this 

 regional metamorphism of increasing intensity would have been 

 equally apparent without the presence of the Cruachan granite. 

 That granite has nevertheless been a factor in determining the 

 suddenness of the metamorphism, where it has invaded rocks so 

 little altered that they have readily lent themselves to the processes 

 of contact-metamorphism which rocks in a more advanced state of 

 crystallization have been able to resist. 



In this paper I have been dealing with the progressive meta- 

 morphism of beds along their strike, but in the same area we have 

 ample evidence of an increasing metamorphism of the same beds when 

 followed across the strike. A traverse from Loch Melfort to Loch 

 Fyne crosses the strike of the beds that I have been describing in the 

 Loch Awe basin. The Loch Awe beds are iu this district lying in 

 a gentle trough of the Ardrishaig Series, which flank them on either 

 gide — the Ardrishaig phyllites occurring on the shores of Loch 



