424 MR. E. M. ANDERSON ON THE GEOLOGY OF [vol. lxxix, 



quote. Certain other points which have a hearing on the geology 

 of the area dealt with here are discussed in a paper which was 

 recently presented by Mr. Bailey to this Society. 1 



In the Geological Survey Memoir 3 which accompanies the pub- 

 lished map of this and the surrounding districts in Perthshire 

 (1-inch Sheet 55, Scotland) the following (Dalradian) sequence is 

 recognized : — 



f Quartzite and quartz- schist with pebbly conglomerate. 

 J Schichallion Conglomerate ('Boulder Bed'). 

 | Limestone (' Blair Atholl '). 

 ^Black Schist. 



Phyllites, etc. ('Ben Lawers Schist'). 



Garnetiferous mica-schist. 



Limestone (' Loch Tay '). 



G-arnetiferous mica-schists (' Pitlochry Schists '). 



Green Beds. 



Schistose grits (' Ben Ledi Grits and Schists '). 



The four members included in the bracket were supposed to be 

 the only part that was present in the Schichallion district. Of 

 this sequence the Quartzite was taken to be the upper limit, and 

 the latest in point of time, with an unconformity at its base which 

 caused it to rest upon either conglomerate, limestone, black schist, 

 or phyllites. 



I do not, in the present paper, propose to discuss the remainder 

 of the sequence. It was taken to be in normal descending order, 

 down to the Ben Ledi Grits. A more or less vertical belt of black 

 schist, with an associated dark limestone, runs across much of the 

 1-inch sheet, and separates the main Quartzite outcrop which lies 

 on the north-west from a Ben Lawers Schist area on the south- 

 east. There can be no doubt that the sequence Quartzite — Black 

 Schist — Ben Lawers Schist, Avhich is seen along this belt, is con- 

 tinued south-eastwards, in the order given in the Memoir, to the 

 Ben Ledi Grits. From the Ben Lawers Schist to the Grits it is a 

 descending structural sequence, 3 of which the lowest members come 

 to the surface on the south-east. 



North-west of the belt of black schist just mentioned, matters 

 are much more in dispute. This belt is highly graphitic in 

 character, and shows a type of slaty cleavage which is absent 

 from most of the rocks in the district. Black lustrous surfaces, 

 developed along the cleavage, and usually at a slight angle to the 

 sedimentaiy banding, are typical of this zone. The belt forms the 

 summit of Ben Eagach, 9 miles east of Schichallion, and any 

 black schist which is certainly on this horizon will be designated 

 Ben Eagach Schist. Mr. G. Barrow, while accepting the 

 Survey view that the Quartzite is later than the Ben Eagach 



1 ' The Structure of the South-West Highlands of Scotland ' Q. J. G. S. 

 vol. lxxviii (1922) p. 82. 



2 ' The Geology of the Country round Blair Atholl, Pitlochry, & Aberfeldy ' 

 1905. 



3 This statement does not apply without qualification to other 1-inch sheets 

 of the Geological Survey map. 



