132 BATHYMETRICAL SURVEY OF 



In the central part of the metamorphic area there is a well-defined 

 line extending from Ben Vrackie south-west by Ben Lawers to Glen 

 Lochay, which marks the axis of a fan-shaped arrangement of the 

 folding of the strata. Along this line the axial planes of the folds are 

 vertical, and on either side they are inclined towards the centre of the 

 fan. Hence on the south-east side of this central axis there is a 

 remarkably persistent dip of the folds towards the north-west, while 

 on the north-west side the general inclination is towards the south-east. 

 A fine example of the latter is to be found in the river Garry, where 

 between Blair Atholl and Dalnaspidal the granulitic schists of the 

 Moine series dip persistently towards the south-east for a distance 

 of about 15 miles, and yet it is highly probable that the same 

 bands are repeated indefinitely by means of folding. This remarkable 

 reduplication of the strata can be clearly demonstrated in the case of 

 the black schist, limestone, and quartzite groups, where the lithological 

 types are clearly differentiated from each other. For a distance of 

 6 miles across the strike, between Ben Vrackie and Glen Tilt, these 

 groups constantly reappear, the sill of garnetiferous hornblende-schist 

 being indefinitely repeated with the black schist. 



Reference has already been made to the system of north-east and 

 south-west dislocations which traverse the metamorphic area. Of these, 

 apparently the most powerful is the Loch Tay fault, which has been 

 traced from near Blair Atholl, across Loch Tay, Loch Earn, and Loch 

 Lubnaig, till it is truncated by the fault along the Highland border at 

 Aberfoil. Further west, and roughly parallel with the foregoing, comes 

 the line of disruption which extends from Loch Garry across Loch 

 Rannoch and the valleys of the Lyon, the Lochay, and the Dochart 

 towards the Braes of Balquhidder. Again, from Tyndrum another 

 dislocation has been followed north-east by Loch Lyon and the west 

 margin of Loch Rannoch in the direction of Loch Ericht. Finally, in 

 the north-west part of the basin there is a line of fracture running along 

 Loch Ericht and Loch Laidon, which is roughly parallel with the Loch 

 Tay fault. In the case of the Loch Tay, th Loch Garry, and the Loch 

 Lyon dislocations, the downthrow has been on their western side; in 

 other words, on that side the outcrops of the sedimentary bands and 

 epidiorite sills have been shifted further to the south by each fault in 

 turn. 



Within the metamorphic area, as already indicated, there are 

 various masses of igneous rock which are later than the folding and 

 foliation of the crystalline schists, and have been referred to the newer 

 granite intrusions of the Highlands. Of these, the most important is 

 the large mass of diorite on the Moor of Rannoch, which stretches 

 northwards to Loch Ericht and west towards Loch Treig, boulders of 

 which have been carried far during the glaciation of the region. Other 

 masses appear on both sides of Loch Ericht, in Glen Tilt, on the lofty 



