Vol. 52.] FOLIATED GRANITES IN EASTERN SUTHERLAND. 645 



felting and amalgamation come on only in the Kinbracc gneisses. 

 It is clear, therefore, that even allowing that the structure of the 

 wavy mica-schists may have been favourable to these types of 

 injection, the following phenomena are coincident : — 



a. Increase in quantity of granite. 



/3. Intimacy of relation. 



y. Increase of coarseness of crystalline texture in the schists. 



L Appearance and perfection of crystallization of sillimanite. 



Y. Summary and Conclusions. 



The foregoing facts suggest important considerations with regard 

 to the nature of intrusion, foliation, and metamorphism. 



It is certain that sedimentary rocks enter into the crystalb'ue 

 complex, but igneous • contact ' in the ordinary sense cannot be held 

 to be the sole cause of the regional metamorphism. Fo^ schists 

 closely resembling some of these (especially Gioup 2 of Kildonan) 

 cover large areas in which no granite is to be see a (see the descrip- 

 tion of the schists above the Moine Thrust-plane in Geol. Surv. 

 Report on N.W. Highlands, Quart. Journ. Geol. Soc. vol. xliv. 

 1888, p. 378). The whole series, however, is powerfully folded, 

 and can be shown to have been subjected to shearing stresses, 

 which perhaps points to the initial cause of metamorphism. That 

 the granitic injections were closely associated with the meta- 

 morphic processes we have little doubt ; but it appears probable 

 that they found the schists already crystalline. 



"What part ' contact-metamorphism' actually played is not perfectly 

 clear. It is true that as we pass from Kildonan, where granites 

 are small and few, to Kinbrace, where they are numerous and large, 

 we do find what has generally been called a ' progressive meta- 

 morphism ' in all rocks which could be expected to show it ; that 

 the intrusive relations at the same time become more and more 

 intimate ; and that sillimanite appears as we pass in, and is most 

 beautifully crystallized in the final stages. From which it seems 

 reasonable to infer that the cause which brought about the intro- 

 duction of the granite also resulted in these high and peculiar 

 types of crystallization. 



Of foliation in the granites there are several conceivable causes. 

 Many of the parallel structures are certainly the remains of biotite- 

 folia belonging to gneisses whose quartzo-felspathic elements have 

 been incorporated with those of the granite, for every gradation can 

 be traced from inclusions retaining their natural orientation (fig. 4, 

 p. 646) down to the merest trains of mica-flakes. Probaoly much 

 of the foliation is of this nature, at any rate where the gneisses 

 lent themselves readily to it. But neither this nor dynamo-meta- 

 morphism can always be appealed to. The numerous cases where the 

 foliation of the granites can be seen to truncate that of the gneiss 

 must be borne in mind. How difficult it would bo to distinguish 

 this from the other structure in cases where transgressivo junctions 

 cannot be observed, the margins consisting of ranges of lenticles I 



