THE FRESH- WATER LOCHS OF SCOTLAND 
131 
The Blair Atholl limestone has an important development in the 
neighbourhood of Blair Atholl, and up the valley of the Tilt towards 
the limit of the basin. Sharing in all the folds of the associated 
phyllites and black schists (group 9), its outcrop is irregular and 
involved. Where these zones appear, in the Tilt, in the Tay, and 
Strath Tummel, they generally give rise to softer outlines than the 
quartzite which apparently overlies them. 
The Perthshire quartzite (group 11) is, perhaps, the most striking 
geological sub-division in the metamorphic series of the Eastern 
Highlands, from its greater durability and the lofty mountains to which 
it has given rise. Along its northern margin the rock is more or less 
coarse-grained, due to the presence of pebbles of quartz and felspar, 
but this band is repeatedly brought to the surface by means of folding. 
An interesting feature of this group is the presence of a conglomerate 
or boulder bed with rounded blocks of granite, foreign to the area, the 
matrix of which seems to vary with the rock in contact with it. Some- 
times appearing as lenticular or boat-shaped masses surrounded by 
black schists, phyllite, or limestone, and again as narrow belts traceable 
for several miles, the quartzite is always one of the dominant features 
of the landscape, occasionally forming lofty peaks, as in Ben-y-Ghlo 
and Schichallion. 
In addition to the sub-divisions of the metamorphic rocks of the 
Eastern Highlands which have just been described, there is a group of 
crystalline schists termed the Moine series ” by the Geological 
Survey, which have a wide distribution in the north-west part of the 
Tay basin. Their lithological characters are remarkably persistent over 
wide areas. Consisting mainly of quartzose granulitic schists or fine- 
grained gneisses with bands of mica-schist, they represent without 
doubt a highly altered series of sediments, the original clastic grains 
of which have been destroyed. They form nearly the whole of the area 
north of Loch Bannoch, up Glen Garry, and northward of Glen Tilt. 
Reference has already been made to the intrusive sheets of basic 
igneous rock which appear in association with the Green Beds and Loch 
Tay limestone, but others occur in connection with the zones of calc- 
sericite schist and black schist. Perhaps the most remarkable example 
of the latter is the mass of epidiorite and hornblende-schist on Ben 
Vrackie north of Pitlochry, where the altered sediments have been 
deflected and bent round the laccolitic intrusion. 
The acid igneous rocks which were injected into the sedimentary 
series, before the folding and development of schistosity in the latter, 
are best represented by the foliated granite of Ben Vuroch, north-east 
of Ben Vrackie. On the north-west slope of that mountain, the 
sediments, which still retain their original bedding, have undergone 
contact alteration, the calcareous shales having been converted into 
calc-silicate hornfels. 
