[ 464 ] 

 XL VI. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 

 [Continued from p. 313.] 



January 25th, 1893.— W. H. Hudleston, Esq., M.A., F.R.S., 



President, in the Chair. 



PTTEE following communications were read : — 

 -*■ 1. " On Inclusions of Tertiary Granite in the Gabbro of the 

 ^uilin Hills, Skye ; and on the Products resulting from the Partial 

 Fusion of the Acid by the Basic Rock." By Prof. J. W. Judd, 

 F.R.S., V.P.G.S. 



The author first calls attention to previous literature bearing on 

 the subject of the extreme metamorphism of fragments of one 

 igneous rock which have been caught up and enveloped in the 

 products of a later eruption. The observations of Fischer, Lehmann j 

 Phillips, Werveke, Sandberger, Lacroix, Hussak, GraefT, Bonney, 

 Sauer, and others show that, while the porphyritic crystals of such 

 altered rocks exhibit characteristic modifications, the fused ground- 

 mass may have developed in it striking spherulitic structures. 



On the north-east side of Loch Coruiskh, in Skye, there may be 

 seen on a ridge known as I)ruim-an-Eidhne, which rises to a little 

 over 1000 feet above the sea, a very interesting junction of the 

 granitic rocks of the Red Mountains with the gabbros of the Cuilin 

 Hills. At this place, inclusions of the granitic rock, sometimes 

 having an area of several square yards, are found to be com- 

 pletely enveloped in the mass of the gabbro. The basic rock here 

 exhibits all its ordinary characters, being a gabbro passing into a 

 norite, traversed by numerous segregation-veins ; the acid rock is an 

 augite-granite, exhibiting the micropegmatitic (' granophyric ') and 

 the drusy (' miarolitic ? ) structures, and it passes in places into an 

 ordinary quartz-felsite (' quartz-porphyry '). 



"Within the inclusions, however, the acid rock is seen to have 

 undergone great alteration from partial fusion, and it has acquired 

 the compact texture and splintery fracture of a rhyolite ; weathered 

 surfaces of this rock are found to exhibit the most remarkable 

 banded and spherulitic structures. 



Microscopic study of the rock of these inclusions shows that the 

 phenocrysts of quartz and felspar remain intact, but exhibit all the 

 well-known effects of the action of a molten glassy magma upon 

 them. The pyroxene, however, has been more profoundly affected, 

 and has broken up into magnetite and other secondary minerals. 

 The micropegmatitic groundmass, which was the last portion of 

 the rock to consolidate, has for the most part been completely 

 fused, and in some places has actually flowed. In the glassy 

 mass thus formed, the most beautiful spherulitic growths have 

 been developed, the individual spherulites varying in size from 

 a pin's head to a small orange. These spherulites are often 



