part I] TIIK SCHISTS OF THE SCHICHALLION DISTRICT. 4--J9 



appear in the comparatively unaltered rocks of the Lochawe 

 Syncline, but seems to be a very widespread characteristic of those 

 parts of Northern Scotland where the metamorphism has reached 

 a somewhat higher stage. I have previously described it as 

 follows (in 'The Gr3olog i y of Mid-Strathspey and Strathdearn ' 

 Mem. Geol. Surv. 1915, p. 22) :— 



' .... a sort of striation visible on practically any well- exposed divisional 

 or bedding-plane of the granulites. This is not rodding in the sense of any 

 actual elongation of the minerals, though the mica-flakes are all arranged so 

 as to have one direction parallel to that of the striation. It seems rather to 

 be due to a minute corrugation of the micaceous laminaa, the folds of which 

 have their axes parallel to the striations. It is none the less probably caused 

 by stretching, and the striations probably coincide with the direction of 

 shear. The impression produced on an observer is that the shearing must 

 have been intense.' 



I also noted that this lineation could be seen to be parallel over 

 wide districts, even where the bedding changes strike. This is 

 well illustrated in the Schichallion district. Throughout the whole 

 of the ' syncline,' and the neighbouring parts of the flagstone 

 series, the linear foliation dips at gentle angles (see map, p. -1-10) 

 southwards : it is thus usually parallel to the strike. Where, 

 however, the latter alters to east and west, south of the Errochty 

 Water, the direction of the former is unchanged. It may be 

 further noted that the direction and dip of the lineation is almost 

 invariably that of the pitch of the smaller folds. Thus, certain 

 folds which affect the Grey Limestone, in the area of east-and-west 

 strike just mentioned, and are shown on the map, pitch at low 

 angles southwards. 



In one respect the description quoted above requires to be modified 

 as regards the Schichallion district. In the micaceous rocks the 

 phenomena are the same ; but in the hornblende-schists there is 

 actual rodding or elongation of the crystals, which always follows 

 the general direction. Tourmaline-crystals, where formed, have 

 also a sub-parallel arrangement: this is shown by a slide of the 

 matrix of the Boulder Bed. Kyanite-crystals, on the other hand, 

 are arranged in the plane of general foliation ; but their directions 

 of maximum elongation lie haphazard in this plane. This is well 

 seen in a tributary of the Errochty Water, which joins it from the 

 south about half a mile above the AUt Choin. The same stream- 

 section shows rodded hornblende-schists. 



South of the Tuinmel the lineation curves round gradually, in 

 conformity with the change of strike, and dips in general eastwards 

 or south-eastwards. I believe this appearance to have been pro- 

 duced somewhat after the manner of a flow-structure ; but, what- 

 ever be its cause, it seems to be a phenomenon worthy of further 

 study, and one that may throw some light on the origin of the 

 Scottish schists. 



q. J. G.S No. 316, 2h 



