418 



THE CRYSTALLINE SCHISTS 



the more massive beds, and to have suffered intense metamorphism, the 

 foliation-planes having been folded and twisted to an almost inconceivable 

 extent. This is well seen in the mountains N. of Loch Taj and along 

 Loch Fyne. Geographically this zone may be traced through the summits of 

 Ben Lawers, Craig Na Calliach, and on to the high ground separating Glen 

 Lochy and Glen Dochart. At Tyndrum it is faulted against the central 

 Highland quartzites, whence it runs N.E. towards Loch Lyon, and it is also 

 well exposed along both the E. and W. shores of Loch Fyne. 



Succeeding the Upper Argillaceous zone and covering a great "part of the 

 central Highlands there is a group of quartzites and limestones here 

 named the Upper Arenaceous zone, because of the predominance in it of 

 the quartzites. It can be seen in the neighbourhood of Blair Atholl, the 

 limestones being well exposed in Glen Tilt, whence they can be traced 

 westwards through Schiehallion, Glen Lyon, the Black Mount, and Dalmally, 

 to the shores of Loch Awe. 



Associated with these different zones are other schists which have origin- 

 ally been intruded into the sedimentary schists as sills of igneous rock, 

 prior to the general metamorphism of the region. These have suffered along 

 with the clastic rocks, and are now known as epidiorites and hornblende 

 schists. A remarkable development of them is to be found along the horizon 

 of the Loch Tay limestone, and in the schists immediately above and below it. 

 Though they now in many instances present a perfectly developed schistose 

 structure, they have originally been igneous rocks of a basic character. Ser- 

 pentines and chlorite-schists, both, probably, of igneous origin, occur here and 

 there throughout the area. 



The following table gives the principal schist-zones, with their character- 

 istic rocks. For reasons to be afterwards shown it is probable that the 

 order given in the table is a descending one, the newest rocks being placed 

 at the top, the oldest at the bottom : 



c 



i t 



to 







f-t 



O 



a 



<D 



03 



- 



,-H 



'o 



02 



VI. Upper Arenaceous zone 



V. Upper Argillaceous zone 



IV. GarnetiferouH schist zone 



TABLE OF THE METAMORPHIC ROCKS OF THE SOUTHERN HIGHLANDS. 



'Dark Schist. 



Limestone. 



Boulder Bed. 



Quartzite. 

 fGrraphite-schist. 

 f Phyllites. 

 j Schistose-quartzite. 

 [Calcareous Serecite-schists. 

 f Garnetiferous Mica-schist. 

 \ Quartz-schists. 

 [Mica-schists. 



TTT T u TI T f Limestones. 



III. Loch Tay Limestone zone s /-, , ^ T - ,-, 



[Calcareous Mica-schists. 



'Green Beds. 



II. Lower Arenaceous zone 



Mica-schists. 



I 



"I Grits and Conglomerates. 

 l( 



o 



I. Lower Argillaceous zone 



. / Hornblende-schists. 

 ^ J Epidiorites. 

 ] Serpentine. 

 I Chlorite-schist. 



Greywackes. 

 fSlates. 

 Phyllites. 

 Grits. 



Greywackes. 

 Thin Limestones. 



