40 BATHYMETRICAL SURVEY OF 



belong to the lower Old Red Sandstone formation, comprising, next the 

 fault, andesitic lavas and agglomerates well seen in the Kelty water. 

 Further to the south-east there is a broad belt of conglomerate arranged 

 in beds, which are inverted or vertical near the fault, and as the 

 observer approaches the plain they dip towards the south-east and 

 pass underneath the overlying red sandstones. 



On the north-west side of this great boundary fault of the High- 

 lands there is a narrow strip of sedimentary rocks about half a mile in 

 breadth, referred provisionally to the Arenig division of the Silurian 

 system, and consisting of red and black shales, radiolarian cherts, lime- 

 stones, and grits. 



To the north of this belt of doubtful strata, the whole of the area 

 included in the geological map accompanying this paper is occupied by 

 rocks grouped under the general term of the crystalline schists of the 

 Highlands. The latter are arranged in a definite order, but as yet it 

 is uncertain whether it indicates the original sequence of deposition. 

 The groups are here given in apparent descending order 



7. Garnetiferous mica-schists. 



6. Loch Tay limestone with sills of epidiorite. 



5. Mica-schists with sills of epidiorite. 



4. Schistose epidotic grits (" Green Beds "). 



3. Ben Ledi grits, massive and sometimes schistose. 



2. Aberfoil slates with subordinate bands of grit. 



1. Leny and Aberfoil grit. 



For a distance of about 5 miles northwards from the great boundary 

 fault, the members of groups 1 to 4 are arranged in more or less parallel 

 belts or strips running south-west and north-east, the strata dipping 

 at high angles to the north-west. The groups appear in consecutive 

 order, the Leny and Aberfoil grit being exposed immediately to the 

 north of the doubtful Arenig rocks, while the Aberfoil slates and Ben 

 Ledi grits appear successively to the north. The schistose epidotic 

 grits (group 4), which lie apparently at the top of the Ben Ledi grits, 

 are developed still further to the north, being traceable from a point 

 not far to the south of Ben Lomond, north-east by Loch Chon and the 

 lower part of Loch Katrine, thence across the hills to Strathyre and 

 Loch Voil. From the Braes of Balquhidder they can be followed north- 

 wards to Glen Dochart, and they reappear in Glen Falloch in the 

 extreme north-west part of the map. At the head of Loch Lubnaig 

 and in the Braes of Balquhidder sills or intrusive sheets of epidiorite 

 occur at no great distance from the " Green Beds." 



In the belt between Loch Chon and Loch Lubnaig the " Green 

 Beds," together with the Ben Ledi grits, form a series of compound 

 synclinal folds, the strata being inclined at high angles. To the north 

 and west of the " Green Beds " the representatives of the Ben Ledi 



