part 4] THE SCHISTS OF THE SCHICHALLION DISTRICT. 441 



VIII. Summary and Conclusions. 



So many debatable points have been dealt with in this account 

 of the district that it may be well, in summarizing the results, to 

 separate those for which the evidence seems clear from those 

 which are to some extent conjectural. 



(1) Among the former results are those which have to do with 

 the Dalradian succession. The facts outlined in this paper, and 

 shown in a general w&j on the map, suggest the following con- 

 clusions : — 



(a) The quartzite, previously taken to be a single unit, is in reality a 



composite group. It contains a central mica-schist and marginal 

 components which are quartzites of different characters. 



(b) On the one side of the quartzite group is a graphite- schist, and a 



succession following this in the order previously determined by the 

 Geological Survey. 



(c) On the other side is the Boulder Bed, and a succession following it as 



given in the table (p. 427). 



It is very difficult indeed to escape these deductions. 



(2) The study of the Boulder Bed has led to a further con- 

 elusion : namely, that the Grey Schist is probably the oldest 

 member, and the Ben Ledi Grits the youngest member of the 

 succession as stated. The validity of the evidence depends, to 

 some extent, on the assumption that the Boulder Bed is a tillite, 

 and while, with others, I favour this assumption, I do not claim 

 that an inference derived from it can as yet be regarded as proof. 



(3) A certain amount of local discordance is associated Avith the 

 Scbichallion Boulder Bed. The facts may be explained by sup- 

 posing that the conglomerate was formed on, and more or less at 

 the expense of, an already partly eroded surface of White Lime- 

 stone and Banded Series, and was afterwards overlapped by the 

 Scbichallion Quartzite. 



(4) The structure of the district is more obscure than the 

 stratigraphy. It is obvious that the folding has been extremely 

 complex. Such complexity might have been produced from a rock 

 originally in horizontal layers, if it had been acted on by a move- 

 ment analogous to How. It is necessary to suppose that this 

 flow-movement itself was complex, although it may have been 

 roughly parallel in direction over areas which extended for several 

 miles. The field appearance known as linear foliation may be 

 the visible indication of such a flow. 



It is almost certain that in the Schichallion district, as in the 

 country nearer Loch Awe, the general relation of the Dalradian 

 Series to the Struan Flags is one of superposition. In a part at 

 least of the district here described the supposed later members 

 of the Dalradian succession overlie in the same general manner the 

 supposed earlier members, and, speaking broadly, the sequence is 

 probably unin verted. 



The line of junction between the Dalradian Series and the flags 



2h2 



