230 THE BASIC AND ACID KOCKS [May 1 894, 



When the Author added that banded and spherulitic rhyolites 

 are often found constituting the margins and apophyses of granitic 

 bosses, he felt, however, unable to follow him ; and the statement 

 that it was such banded and spherulitic rhyolites which form the 

 dykes, supposed to be apophyses of the granite, suggested to him 

 grave reasons for doubting the interpretation of the phenomena 

 put forward by the Author of the paper. The Author had pointed 

 out the existence of a dyke-like mass of the banded and spherulitic 

 xhyolite in the very midst of the granite of Meall Dearg, and he had 

 admitted that this might possibly constitute a later intrusion than 

 the granite itself. But if this were the case with the rhyolite in 

 the midst of the granite, might it not also be equally true of the 

 rhyolite in the peripheral portions of the same mass ? The granting 

 of this, however, would at once destroy the argument based on the 

 statement that the granite itself sends offshoots into the gabbros. 

 This was only one of several ways in which the appearances might 

 be interpreted, without accepting the conclusions of the Author of 

 the paper. 



But while there was this uncertainty about the evidence of veins — 

 and corresponding differences of opinion on the bearings of this class 

 of evidence had been exhibited among competent observers, in the 

 case of two previous discussions before the Society, the rival views 

 being supported by a similar display of diagrams and photographs — 

 there could be no doubt whatever as to the evidence of included 

 fragments. The speaker exhibited hand-specimens taken from 

 masses which were completely surrounded by the gabbro. The 

 centres of these specimens consist of the normal micropegmatitic 

 granite (' granophyre ') of the district, the fused outer coating dis- 

 playing all those phenomena which have been so well described by 

 Lefiinann, Bonney, Sauerf Biickstrom, and other petrologists, as 

 belonging to masses of acid rocks that have been caught up and 

 enveloped in basic ones. In opposition to the Author of the paper, 

 the speaker maintained that the demonstration of a single case of 

 one rock being enclosed in another was proof positive as to their 

 relative age. With respect to the specimens on which he relied, 

 and the sections cut from them, he offered to submit his whole case 

 to the three petrologists of the Geological Survey — in whose judg- 

 ment and fairness he had the most perfect confidence. 



The Author, in reply, remarked that Prof. Judd had left the 

 essential part of the paper unanswered. It was beside the question 

 to bring up the observations of earlier geologists. No amount of 

 such testimony could avail in the teeth of plain facts. Prof. Judd 

 had affirmed in his last paper that the presence of inclusions of 

 granite in the gabbro was absolutely irreconcilable with the 

 existence of veins of the same granite cutting the gabbro. But it 

 must obviously be just as true that the presence of dykes of granite 

 (or granophyre) cutting the gabbro is absolutely irreconcilable 

 with the existence of inclusions of the same acid rock in the basic 

 series. Prof. Judd had brought forward no evidence that his 

 ' inclusions ' were really such ; but he (the Author) had adduced in 



