420 ME. E. M. AXDERSOX OX THE GEOLOGY OF [vol. lxxix, 



basic igneous rock, irregularly introduced among the sediments. 

 There is, however, one point near the summit of Creag an Fhithich 

 (three-quarters of a mile south-south-east of Kinloch Kannoch) 

 where the succession ? Ben Lawers Schist — graphite-schist — pebbly 

 quartzite is clearly visible. The correlation of the graphitic rock 

 with the Ben Eagach Schist is, therefore, almost certainly justified, 

 and it should be noted that the occurrence in this area both of 

 Ben Lawers Schist and of ' Black Schist ' had been suspected by 

 Mr. Grant Wilson. 



The two belts of grey mica-schist and the two belts of non- 

 pebbly quartzite are fairly persistent, as each is traceable for 5 or 

 6 miles in a curving course, with certain variations of thickness^ 

 The dips are nearly always steep, and sometimes vertical. As the 

 Central Highland Quartzite has always been taken to include the 

 rock which forms Schichallion, these facts seem to justify the con- 

 clusion that the former does not consist of one member, but is a 

 composite group. A fivefold division might seem to be indicated, 

 but against this view must be noted the great similarity of the 

 rock composing the two belts of mica-schist. The two belts of 

 non-pebbly quartzite are also indistinguishable in character, and 

 this suggests that only three members are present, two of which 

 are repeated by folding or some line of disruption. More con- 

 vincing evidence of the division being only threefold had been 

 obtained by Mr. Bailey in the Loch Tummel and Killiekrankie 

 districts before I had mapped this part of the ground, and, relying 

 on his so far unpublished work, I have divided the Quartzite 

 Group into three, as shown in the table (p. 427). The non- 

 pebbly and pebbly quartzites may be appropriately named the 

 Schichallion Quartzite and the Cam Mairg Quartzite, 

 while the mica-schist division has been named Irv Mr. Bailey the 

 Killiekrankie Schist. 



Turning next to the further side of the Quartzite, we may note 

 that the non -pebbly band which forms the higher parts of 

 Schichallion can be traced at least as far as the southern slopes of 

 Beinn a' Chuallaich. For all this distance it has the grey mica- 

 schist (Killiekrankie Schist) on the south and west, and the well- 

 known Schichallion Boulder Bed on the east and north. The 

 three formations are jointly affected by a change of dip which 

 takes place west of Schichallion. In that mountain itself the 

 Boulder Bed dips under the Quartzite, while farther north the 

 Killiekrankie Schist and Quartzite dip more or less steeply under 

 the Boulder Bed. 



There is thus, I think, clear evidence, not only that the 

 Quartzite in this district has separate ' edges ' : that is, both top 

 and bottom, but also that the Boulder Bed is on the opposite side 

 of the Quartzite from the Ben Eagach Schist and the remaining 

 members of the Southern Perthshire succession. This conclusion, 

 founded on what has been observed in the district under discussion, 

 lends strong support to one part of the views put forward by 

 Mr. Barrow with resrard to the succession somewhat farther east. 



