THE FRESH-WATER LOCHS OF SCOTLAND. 129 



7. Garnetiferous mica-schists. 



6. Loch Tay limestone. 



5. Garnetiferous mica-schists of Pitlochry. 



4. Hornblende-schists of clastic origin and epidote-chlorite schists 



(Green Beds). 



3. Schistose grits (Ben Ledi grits and schists). 



2. Dunkeld slates. 



1. Schistose grits next the Highland fault. 



The members of the metamorphic series have been injected by sheets 

 and bosses of acid and basic igneous materials, which have shared in 

 the folding and schistosity of the altered sediments into which they 

 have been intruded. 



The distribution of these various groups of altered sedimentary 

 strata, and the intrusive sheets of basic igneous material (epidiorite 

 and hornblende-schist), have had an important influence in determining 

 the trend of the tributary valleys and their surface features. The sub- 

 divisions given in the above table form sub-parallel belts crossing the 

 basin in an east-north-east and west-south-west direction, the outcrops 

 of which have been affected by several powerful faults, to be referred to 

 presently. 



Beginning at the Highland border, we find immediately to the north 

 of the marginal fault a narrow band of schistose grits, extending from 

 the river Almond to Birnam wood on the Tay, which may represent the 

 Leny and Aberfoil grit of the Callander district. Next in order comes 

 a zone of slate, traceable almost continuously from the forest of Glen 

 Artney, by Comrie, to a point south of Dunkeld, where it is exposed 

 in various quarries. The Ben Ledi grits and schists, which, as they are 

 followed northwards, become more schistose and highly crystalline, 

 form a belt several miles in width, extending across the basin from the 

 heights round Loch Earn, north-eastwards by the Almond, Strath 

 Bran, and the Tay between Birnam Hill and Logierait, and onwards by 

 Strath Ardle to Kirkton of Glen Isla. Over much of the area where 

 the metamorphism is not highly developed the schistose grits of this 

 group give rise to prominent rock features. 



The Ben Ledi grits are followed northwards by an important zone 

 of epidote-chlorite schists (Green Beds), which, in their ultimate stage 

 of alteration, merge into hornblende-schists that are almost indis- 

 tinguishable from rocks of this type of igneous origin. They are usually 

 associated with intrusive sheets of epidiorite that pass into hornblende- 

 schists, the latter sharing in the folding and schistosity that have 

 affected the Green Beds. Like the members of this zone in the 

 Callander region, these epidote-chlorite schists and accompanying sills 

 of epidiorite form prominent rock features in the landscape, which 

 have more successfully resisted glacial erosion than the overlying zone of 



K 



