130 BATHYMETRICAL SURVEY OF 



garnetiferous mica-schist. On both sides of the valley of the Tay at 

 Aberfeldy these rocks may be studied, and they appear on the moor- 

 land between the Tay and Strath Ardle, and eastwards by Kirkton of 

 Glen Isla, either as isolated patches in the form of outliers, or as more 

 or less continuous outcrops. Again, towards the south-west, the Green 

 Beds reappear at intervals on the heights between Loch Tay and Loch 

 Earn till they are abruptly truncated by the Loch Tay fault. 



One of the best-defined zones in the metamorphic series of the 

 Eastern Highlands is that of the Loch Tay limestone, with its overlying 

 and underlying garnetiferous mica-schists. In the Tay basin the 

 members of these groups (5, 6, 7) usually indicate a stage of high 

 metamorphism, the beds being easily eroded by surface agencies. Save 

 where deflected by powerful faults, their outcrops are traceable almost 

 across the basin. From Glen Fernate, at the head of Strath Ardle, the 

 Loch Tay limestone has been followed south-westwards, by Pitlochry, 

 along the north slope of the Tay valley at Aberfeldy, to the heights 

 overlooking Fortingal, where the outcrop has been deflected by the 

 Loch Tay fault. West of this line of disruption the limestone reappears, 

 about 4 miles further south, on both sides of Loch Tay (see geological 

 map), whence it can be traced westwards up Glen Dochart and across 

 Strath Fillan almost to the slopes of Ben Lui, at the south-west 

 margin of the Tay basin. Owing to folding, the Loch Tay limestone 

 and its associated strata reappear to the north of the line of outcrop 

 just indicated, as, for instance, in Glen Lyon and in the valley of the 

 Lochay north-west of Killin; and to the south of this line, it is met 

 with at Lochearnhead and on the Braes of Balquhidder. An important 

 feature connected with this limestone is the frequent occurrence of a 

 massive sill of epidiorite in conjunction with it. 



Still further north the sub-divisions just described are succeeded by 

 calc-sericite schists, phyllites, and black schists with thin lenticular 

 bands of limestone (groups 8, 9), which present lithological characters 

 that are, as a rule, readily identified. The trend of the outcrop of these 

 zones has been affected by the north-east and south-west faults which 

 traverse the basin, and the black schist spreads over a broad area, in 

 certain localities, by means of sharp isoclinal folds. Taking first the 

 most southerly outcrop of the calc-sericite schist, phyllites, and black 

 schist, they are traceable from Ben Vrackie south-west by Faskally on 

 the Tay, to the Loch Tay fault north of Fortingal. West of this line 

 of disruption, they have been followed from Glen Lyon, by Ben Lawers, 

 and across Glen Lochay to the heights above Glen Dochart, where they 

 terminate in a synclinal fold of the underlying garnetiferous mica- 

 schists associated with the Loch Tay limestone. Still further west they 

 reappear and form a broad outcrop stretching from the upper part 

 of Glen Lyon in a south-south-west direction towards Tyndrum, where 

 they are again interrupted by a north-east and south-west fault (see 

 geological map). 



