part 4] THE SCHISTS OF THE SCHICHALLIOK DISTUICT. 425 



Schist, lias advanced the opinion that the limestone and the 

 associated ' dark or leaden ' schist of the Blair Atholl and Braemar 

 districts are later than the Quartzite, and thus separate from the 

 rocks of the Ben Eagach zone. 1 Mr. Barrow also holds that the 

 Quartzite has upper and nether ' edges ' of distinctly different 

 characters. 



II. Divisions of the Quartzite Group. 



The Ben Eagach belt is laterally shifted by the Loch Tay Fault. 

 West of this displacement the outcrop of black schist is more com- 

 plicated ; but the zone occurs without question on the south side 

 of Cam Mairg. The quartzite which borders the belt is marked 

 by a predominantly pebbly character. Non-pebbly bands occur as 

 alternations, but are nowhere predominant. The pebbles, although 

 sometimes larger, are perhaps most commonly of the size of peas. 

 They consist of quartz and felspar, but those of quartz are most 

 numerous. The higher parts of Cam Mairg show a typical develop- 

 ment of this pebbly quartzite. 



A small area of black schist, on the northern slope of the same 

 hill, is surrounded by the pebbly quartzite, and from its highly 

 graphitic character is certainly an infold of Ben Eagach Schist. 

 This area is on the southern margin of the district which has been 

 investigated, and will be used as a starting-point in the discussion. 



A traverse beginning at this infold, and directed north-north- 

 eastwards, 2 crosses first a zone of pebbly quartzite about a quarter 

 of a mile wide. Following this is a broad belt of a somewhat 

 distinctive grey mica-schist or granulite, with abundance of white 

 mica. After nearly a mile of this pelitic type has been crossed 

 with almost vertical dip, a quartzite is reached, which, from the 

 almost entire absence of pebbles, it is impossible to suppose can be 

 the same as that of Cam Mairg. This quartzite forms a strip 

 running north-west and north, as shown in the map (PI. XXV). 

 Where crossed by the traverse it is flanked on the north-east by 

 another belt of grey mica-schist, exactly similar to that already 

 mentioned, and this again by a broad outcrop of non-pebbly 

 quartzite, which includes in its course the higher parts of Schich- 

 allion. 



Let us now follow these various outcrops along their strike. 

 The Cam Mairg pebbly quartzite continues with steep dips in 

 wedge-shaped fashion to the north, and, although it thins very 

 much, it can be traced to beyond the Biver Tummel. Through 

 the latter part of its course it is bordered on the west by a highly 

 graphitic rock, along with a rock showing segregations of calcite, 

 and containing acicular actinolite-crystals, which resembles certain 

 parts of the ' calc-sericite ' or Ben Lawers Schist. Much of this 

 area is drift-covered, and the geology is further obscured by 

 hornblende-schists which are probably original intrusive masses of 



1 ' On the Moine Gneisses of the East Central Highlands, & their Position 

 in the Highland Sequence ' Q. J. G. S. vol. lx (1904) p. 400. 



' Not precisely along 1 the line AB of the horizontal section (PI. XXV). 



2tt2 



