438 MR. E. M. AXDERSOX ON THE GEOLOGY OF [vol. lxxix, 



that it is along the western margin that it is necessary to suppose 

 the more violent part, or possibly the whole of the discordance. 



The margin of the Struan Flags has now been followed by the 

 Geological Survey staff to near Loch Awe. For most of this 

 distance the flags do not come directly into contact with rocks 

 which belong to the secpience that in this paper has been described 

 as Dalradian. There is an intervening zone, the relations of 

 which have been discussed by Mr. E. B. Bailey & Mr. M. 

 McGregor. 1 When, however, the rocks of the sequence are 

 reached, they belong to the Quartzite Group, or to the Ben 

 Eagach Schist, or to that part of the succession here regarded as 

 later. The Boulder Bed, for certain, does not reappear. It is 

 thus seen that, whatever be the cause of the transgression along 

 the ' syncline ', whether folded fault-line or unconformity, it is a 

 far-reaching, and not a local phenomenon. 



While I favour the hypothesis of a folded line of movement, 

 I do not think that this discontinuity need necessarily have been 

 a thrust-line. A normal fault of large dimensions, which had 

 been subject to intense shear, might explain the phenomena. 

 Such a shear might bring all original structures, including the 

 fault and the bedding, into approximate parallelism. This theory 

 probably implies the necessity of a general overriding movement, 

 along the Dalradian border, which came from either the east or 

 from the south. 



Such a movement might not itself be localized in a thrust- 

 plane, but might act on a pre-existing normal fault so as to 

 produce somewhat similar results. 



VII. Regional Metamorphism. 



The degree of metamorphism has been such as to convert the 

 limestones of the district into rather coarsely crystalline marbles. 

 The argillaceous rocks are partly pelitic gneisses, although in other 

 cases they may be described as schists. It may be noted that 

 garnet is abundant in parts of the Killiekrankie Schist, and also 

 occurs, though more sparingly, in the Grey Schist. Kyanite is 

 frequent, and sometimes forms fairly large crystals, in all the 

 chief pelitic rocks of the district. These include the Killiekrankie 

 Schist, the Grey Schist, and parts of the matrix of the Boulder 

 Bed. The Gvej Schist also contains well formed staurolite in one 

 locality. 



The amount of shear has been great enough to bring the sedi- 

 mentary banding of the different types into general parallelism 

 with the plane-foliation. 



The structure known as 'linear foliation 1 is a common feature in 

 the district, though not more so than in various other parts of the 

 Highlands which I have mapped. This phenomenon does not 



1 Q. J. G. S. vol. lxviii (1912) pp. 172 et seqq. 



