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, the 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 
