Metamorpldsm around the Ross of Mull Granite. 791 



is regarded as one of the ' newer granites'. The rock shows very 

 little evidence of faulting or movement of any kind, and is traversed 

 by sheets of mica-trap. The eastern boundary of the granite is a 

 very intricate line of junction with typical Moine Schists and 

 Gneisses, into which it has been intruded. Injection-breccias 

 occur along the margin, where the granite is crowded with schist- 

 inclusions. 



The changes in the pelitic schists are of two kinds, and are con- 

 sidered under separate headings (a) and (6) below. 



(a) Impregnation. — The schists have been impregnated with 

 the granite in a very intimate manner: — (1) Along irregular 

 cracks ; (2) Along bedding-planes ; (3) Along strain-slip ; and 

 (4) Along foliation. 



Variously banded rocks have been thus produced, which suggest 

 how readily these processes, carried out on a large scale, would 

 convert pelitic sediments from the state of schists into crystalline 

 igneous gneisses. 



(b) Thermal Metamorphism. — In some places the pelitic 

 gneiss in contact with the granite, and commonly the masses in- 

 cluded in the granite, have been very highly altered. The new 

 minerals formed are sillimanite, andnlusite, cordierite, and green 

 spinel ; and these are present in such amount that their formation 

 must have been accompanied by much recrystallization among the 

 quartz, felspar, and mica also. 



Sillimanite is the most abundant new mineral, and occurs not 

 only as fibrolite throughout the rock, but also in larger crystals 

 which are often grouped together in prismatic aggregates. These 

 aggregates weather out as conspicuous knobs, measuring about an 

 inch across. 



Under the microscope, the sillimanite is seen to enclose large 

 numbers of grains of green spinel. The cross-sections of silli- 

 manite are diamond-shaped, and show a pinacoidal cleavage ; their 

 colour between crossed nicols is a very low grey, and good inter- 

 ference-figures are obtained. 



The association of minerals in the schists is the same as that 

 noticed at the margin of the Ben Cruachan ' newer granite '-mass, 

 and also at the margin of ' newer granite ' at Netherly in Elgin. 



Tourmaline, kyanite, and staurolite also occur in the Moine 

 Schists of Mull, but are in no way connected with the granite. 



March 9th.— Prof. W. W. Watts, Sc.D., M.Sc, F.E.S., 



President, in the Chair. 



The following communication was read : — 



' The Carboniferous Succession in Gower (Glamorganshire)/ By 

 Ernest Edward Leslie Dixon, B.Sc, F.G.S., and Arthur Vaughan, 

 B.A., D.Sc, F.G.S. 



The succession in three districts in Gower is described, the 



