Vol. 52.J FOLIATED GRANITES IN EASTERN SUTHERLAND. 649 



was interested to see a large specimen on the table illustrating the 

 fine-grained injection of a rock by granite in thin parallel veins, as 

 it closely resembled Prof. Bonney's ' granulitic series ' at the Lizard, 

 for which the speaker, in his first paper on that region, had sug- 

 gested a similar origin. He felt some difficulty in criticizing the 

 paper on one or two points. The Authors suggested that the 

 ' initial ' metamorphism of the schists into which the granite had 

 intruded was ' perhaps ' due to ' shearing stresses ' ; but the paper, 

 as read, did not disclose any evidence to prove this contention. The 

 hypothesis might or might not be true, but he was not prepared to 

 accept it without sufficient evidence. The metamorphism might be 

 anterior or posterior to the shearing. 



As regards the last point in the paper, the Authors said that the 

 granite was intrusive, but suggested that it was itself a product of 

 the metamorphism of the schists. As the Authors had not attempted 

 to unfold this theory, it would be idle to attempt to criticize it. He 

 would only remark that granite contained highly heated steam, 

 or water, under great pressure, charged with the mineral matter of 

 the granite, and as this solution penetrated into the rocks in con- 

 tact with the granite, they became impregnated with the minerals 

 of the granite, and might thus appear to blend into granite. 



Mr. Teall said that the Authors had clearly proved that • lit par 

 lit' injection and other allied phenomena occurred on an extensive 

 scale in the area in question ; but they wisely refrained from 

 speaking as if they had solved all the problems connected with the 

 origin of the schists of the district. It was a curious fact that in 

 several areas granitic rocks were found to be intrusive into gneissose 

 rocks which closely resembled them in mineralogical composition. 



Speaking on the subject of dynamic metamorphism, he remarked 

 that the rocks into which the granitic magma had been intruded 

 gave abundant evidence of having been folded and sheared — they 

 must at one time have been, so to speak, alive with movement — and 

 he doubted whether a single cubic inch could be found which had not 

 suffered deformation. At the same time the crystalline grains were 

 not fractured, so that crystallization must have taken place during 

 or after the movement. Some critics would apply the theory of 

 dynamic metamorphism only to those rocks which now possessed 

 cataclastic structures ; but this limitation had never been contem- 

 plated or accepted by those who were mainly responsible for its 

 introduction. 



Prof. Johnston-Lavis remarked that the evidence offered by the 

 Authors as to the high temperature of the matrix-rocks into which 

 the granite was injected probably inferred also a comparatively 

 plastic state, which would favour the extraordinarily complicated 

 ribbon-and-vein structure so characteristic of such regions. High 

 temperature and the approach to fluidity of materials are, as is well 

 known, conditions most favourable to chemical interchange and 

 osmotic diffusion, which are further increased by diversity of chemical 

 composition of the matrix and the injected material and by the 

 affinities between the elements of the one and the other. The 



