Vol.51.] GRANOPHYRE AND THE GRAINSGIIX GREISEN. 147 



some rather unnatural zigzags, particularly in the aluminium- and 

 magnesium-lines. 



[Prof. Brogger has pointed out (Vidensk. Skr., math.-naturw. 

 Klasse, 1894, no. 4, p. 196) a misconception underlying my state- 

 ment in Quart. Journ. Geol. Soc. vol. 1. p. 326, that the phenomena 

 of differentiation described hy him ' differ in a fundamental respect ' 

 from those of the Carrock Fell gabhro. He distinguishes two kinds 

 of differentiation, tief-magmatische and laJckolithische ; and the con- 

 trast which I drew should appty only to the former of these. The 

 latter, or, as it is called in his paper on Gran, ' differentiation in the 

 bosses,' is in no essential respect dissimilar to that described by me 

 at Carrock Fell. — January 25th, 1895.] 



EXPLANATION OF PLATE IV. 



Sketch -map of the Carrock Fell district (scale : 3 inches = 1 mile), showing 

 the distribution of the gabbro and diabase and of the granophyre ; also the 

 greisen of Grainsgill. The Skiddaw Slates, the Eycott Lavas (part of the 

 Volcanic Series), and the Drygill Shales (belonging to the Coniston Limestone 

 Group) are left blank. 



The boundaries, especially in the western portion, where exposures are few, 

 are often in part conjectural. The broken lines indicate faults. 



Discussion. 



Sir Archibald Geikie, complimenting the Author upon the skill 

 with which he had worked out his subject, remarked that the 

 summary of the paper, as expounded at the Meeting, was so con- 

 densed that criticism was hardly possible until the full paper was in 

 print. There were only two points on which he would ask for 

 further information. In the first place he wished that the Author 

 would state whether he had any evidence of the date of the gabbro 

 and granophyre-protrusions of Carrock Fell : they were admittedly 

 much younger than the granite and greisen of Skiddaw. In the 

 second place, he asked whether, among the various structures of the 

 granophyre described by Mr. Harker, there was any distribution 

 with reference to position in the body of the rock, and in particular 

 whether any distinctive structures were observable in the marginal 

 portion of the granophyre where it impinged upon the gabbro, which 

 it had partly incorporated into itself. 



Mr. Teall said that he had paid a short visit to the district some 

 time ago, and had come away with the impression that there were 

 transitions from gabbro to granophyre. The Author's more detailed 

 observations proved that he (the speaker) must have been mistaken. 

 He fully agreed with the Author as to the intimate relation between 

 micropegmatitic and spherulitic structures. He considered that the 

 microfelsitic spherulites of Rosenbusch were submicroscopic inter- 

 growths of quartz and felspar. The greisen of Grainsgill appeared 

 to be essentially distinct from that of St. Michael's Mount, Cornwall. 

 The latter contained topaz, and was clearly due to an alteration of 



