part 4] THE SCHISTS OF THE SCHICHALLION DISTRICT. 437 



follows that, from its marginal character, the Grey Schist is the 

 latest of the underlying formations, and the truncation of the 

 different horizons of the Dalradian Series is due to erosion. The 

 following facts may then he noted. The flags in this district con- 

 tain arkoses and gritty quartzose rocks which are occasionally 

 almost to he described as pebbly, but nothing in the nature of a 

 conglomerate. Also, the same type of truncation along the junction 

 as that which has been observed in the Dalradian Series, takes place 

 to a certain extent among the flags. In following the line of 

 contact where it is sharply defined, the marginal member of the 

 Struan Flag Group is first a gritty arkose, which is seen beside the 

 Grey Limestone, at its southernmost exposure on the west side of 

 the 'syncline'. It varies to a semipelitic type, which borders the 

 Grey Schist in the Errochty-Water section. Farther along the 

 boundary the marginal rock consists of typical flags and a flaggy 

 quartzite, as, for instance near Dunalastair ; and lastly, as before 

 mentioned, one encounters a massive quartzite. 



It is, therefore, necessary to suppose that, even on the present 

 hypotheses, there is a certain amount of overlap. It may be argued 

 that, on an uneven floor, one should find in the flagstone series 

 recognizable fragments of the underlying eroded rocks, such as 

 Grey Schist and Grey Limestone. Such fragments are not found, 

 and, as has been previously shown, the late position in the Dalradian 

 sequence, which is assigned to the Grey Schist on the two hypo- 

 theses here set forth, is in itself unlikely. 



If the discordance be due to a plane of movement, there are two 

 ways in which the facts may be regarded. Either the junction 

 with the Grey Schist is a natural one, which terminates against 

 this plane near the northern end of the syncline, or the whole 

 line of contact consists of a folded fault or faults. 



A fact with a possible bearing on the existence of a marginal 

 dislocation has been noted in the Geological Survey Memoir by 

 J. S. Grant Wilson, who writes as follows : — 



' This normal north-east strike is modified in the area between Glen Garry 

 and the Erichdie [Errochty] Water by the lines or narrow belts along which 

 the beds are violently contorted and thrown into a series of sharp vertical 

 folds ; the strike being at right angles to that of the rocks on either side. 

 The most prominent of these lines appears to form the north-east boundary 

 of the Trinafour complex, .... and runs in a W.N.W. direction from Meall 

 Dall-chealach, crossing the Garry at the foot of the Allt Stalcair. It gives 

 rise to a conspicuous feature, forming a ridge which projects above the 

 surrounding moor.' (Op. cit. 1905, pp. 70-71.) 



The facts recorded both on the published map and on Mr. 

 "Wilson's field-map seem, however, to indicate that the line of 

 movement is continued along the western, more probably than 

 along the eastern margin of the Trinafour complex, which means 

 what is here called the 'syncline'. If this be the case, it must bend 

 round so as to become parallel to the strike, and at the same time 

 cease to form any prominent feature. It will have been noticed 



