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 And 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 
