﻿Vol. 66.] METAMORPHISM AROUND THE ROSS OF MULL GRANITE. 399~ 



of thermal alteration, but kyanite had never been found in the 

 Scottish Highlands under circumstances which would lead observers 

 to conclude that it was due to the contact-action of Newer Granites. 

 On the other hand, this mineral occurred not seldom in the vicinity 

 of masses of the Older Granites or granitic gneisses. It was found, 

 for example, in the Archaean inliers which appeared as infolds iu 

 the Moine Schists north of the Great Glen, and in the black schist 

 of Banffshire and Aberdeenshire. In the metamorphic aureole 

 of the Inchbae augen-gneiss, the pelitic Moine Schists had been 

 converted into banded splintery hornfelses, which had for some 

 reason resisted dynamic stresses, while the granite and the un- 

 altered sediments had been converted into gneisses and schists. 

 These hornfelses sometimes contained large crystals of andalusite,. 

 which still preserved their characteristic outlines, but had been 

 changed to aggregates of kyanite. These pseudomorphs indicated 

 that kyanite, which was the silicate of alumina that had the 

 highest specific gravity and lowest molecular volume, tended to 

 replace andalusite in rocks that had been subjected to great 

 pressures. 



Whatever doubts might be advanced regarding the origin of the 

 sillimanite, cordierite, and green spinel in the enclosures of the Ross 

 of Mull granite, there could be no question that these minerals 

 had been produced in the pelitic Moine Schists of the Ross of Mull 

 by the contact-action of Tertiary dolerite sills : for Mr. C. T. 

 Clough had observed that, at the edge of these sills, the mica-schists 

 had in some places been fused to a black glass, which was full of 

 cordierite, sillimanite, and spinel. 



Mr. E. B. Bailey, in speaking to the points raised by the first 

 speaker, remarked upon the general petrographical resemblance 

 of the Ross of Mull granite to the admitted Newer Granites of 

 other parts of the Highlands. This resemblance was strengthened 

 by the occurrence of lamprophyres and porphyrites in connexion 

 with the Ross of Mull granite. It was very difficult, moreover, to 

 reconcile the totally unsheared condition of the granite with the 

 hypothesis that the intrusion was of pre-Cambrian age, considering 

 that it lay only a very short distance to the east of the great 

 Moine Thrust. The a priori objection to the attribution of the 

 granite to a post-Cambrian date was based upon the nature of 

 its margin and of the attendant contact-metamorphism. This 

 objection lost much of its weight, in view of the very similar 

 phenomena observed in connexion with the granites of the Glencoe 

 district, of proved Old Red Sandstone age. 



Dr. J. D. Falconer said that, in the course of the survey of 

 Northern Nigeria, some facts bad been ascertained, which had a 

 certain bearing upon the matter under discussion. In Nigeria 

 there were two sets of granitic intrusions, an earlier and a later, 

 which had invaded a complex of crystalline igneous gneisses and 

 gneisses of sedimentary origin. The later set consisted largely of 

 soda-granites which showed sharp contacts and chilled margins. 

 The earlier set included granites of a more ordinary biotitic and 



