﻿398 METAMOEPHISM AROUND THE EOSS OF MULL GEANITE. [Aug. 1 9 1 O, 



published 1-inch map, as was always done in the case of the Devon 

 and Cornish granites. In two cases at least, this aureole of altera- 

 tion in the Highland rocks, due to new metamorphism by the Newer 

 Granites, was perfectly well known. It did not extend more than 

 3 yards from the granite margin ; and the new rocks produced 

 showed no trace of foliation in the arrangement, of their new 

 minerals. 



Dr. Teall congratulated the Author on having had so interesting 

 a district to work in, and complimented him on the way in which 

 he had presented the results of his observations to the Society. 

 The speaker had himself observed in different parts of Scotland, 

 especially in Caithness, examples of many of the phenomena of 

 intrusion described by the Author ; but he had rarely, if ever, 

 seen them so well displayed as they evidently were in the Ross of 

 Mull. The sillimanite-rocks were certainly finer than any that he 

 had ever seen. 



Referring to the previous speaker's remarks, Dr. Teall said that 

 he was not particularly interested in the age of this granite. The 

 granites of the Highlands belonged to different periods, and, given 

 suitable conditions, any of them might have produced cordierite- 

 sillimanite rocks. The terms older and newer as applied to 

 the granites of the Highlands were not very definite. He presumed 

 that the Author had some reason tor using the latter term in this 

 case. 



Dr. Plett remarked that the Author had shown that, in the Ross 

 of Mull, there was much evidence of a remarkable character bearing 

 on some of the most important problems of Highland geology. 

 The injection and permeation of the schists by the granite were 

 very interesting, and must also be of an uncommon type, as, from 

 the speaker's experience, junctions of this kind were very seldom 

 met with at the margins of the Newer Granites. He hoped soon 

 to have an opportunity of visiting these sections in the field, but 

 the evidence now put before the Society, in photographs and in rock- 

 specimens, had convinced him of the reality of the phenomena. 

 The sillimanite-andalusite rocks in and around the granite were 

 the most completely altered argillaceous sediments that the speaker 

 had ever seen from the Highlands of Scotland, and he had little 

 doubt that they were due to the contact-action of the Ross of Mull 

 granite. It was certainly true that the Newer Granites often 

 produced strikingly little contact-alteration, but instances were 

 known where they had converted even the highly crystalline Moine 

 Schists into cordierite-sillimanite-andalusite rocks. He would cite 

 only one instance, which was discovered by Mr. Hinxman at 

 Netherly (Elgin), and described in the Geological Survey Memoir on 

 Lower Strathspey. There the pelitic Moine Schists were full of 

 cordierite for a distance of a foot or two from the edge of the 

 Netherly diorite, which was one of the basic apophyses of the Ben 

 Rinnes and Hunt Hill granites. 



The kyanite-tourmaline rocks, in the speaker's opinion, were 

 even more interesting. They seemed to him to bear the stamp 



