5<S SUPPLEMENTARY NOTE ON LIMURITE. 



axinite quartz veins, on the West Coast P. A. sections,. 

 close to the granite. A slide prepared from this vein rock 

 shows axinite, quartz, and an abundance of leucoxene. It 

 is noteworthy that the axinite is confined to the vein stuff,. 

 as in Cornwall, but there is no occurrence of limurite. 



Boron vapours, existing in the magma, and evolved 

 during crystallisation, undoubtedly play a part in produc- 

 ing both tourmaline and axinite. In Cornwall both tour- 

 maline and axinite are found in the granite contact zone,, 

 while other rocks, sometimes basic igneous ones, have been 

 acted upon l)y graiiite with the same results. In the 

 Hartz axinite and tourmaline occur at the contact of 

 granite and diabase, and this led Lossen to correlate these 

 tw(j minerals. * In view of these facts, it seems to us very 

 likely that the Western granite or its elvans and the 

 Colel)rook pyroxinite consolidated contemporaneously. . 

 Plutonic solfataric processes, wdiich were plainlj' in opera- 

 tion in the* granite area, as shown by the tourmaline and 

 axinite just referred to, maj' very w^ell have liberated the 

 boron vapours, which, travelling eastwards by easily 

 imaginable channels, arrived at and were entangled in the 

 moving mass which cooled as the axinitic pyroxenite at 

 the Colel^rook. The whole question of this occurrence of 

 axinite possesses a special interest for all occupied with 

 the prol^lems connected with the origin of igneous rocks.- 



Microscopical inspection of the tourmaline-quartz-por- 

 phj'ry at the South Renison Bell mine discloses a ground- 

 mass existing as a Mosaic of quartz and tourmaline, which 

 contains porphyritic crystals of quartz and nests of large 

 tourmaline and quartz crystals. There is no doubt as to 

 the toiu-maline. Its colour is brownish yellow and blue,, 

 often in one and the same crystal, strongly dichroic 

 > E, axis of maximum elasticity || C. The tourmaline 

 often enwraps grains of quartz. The quartz contains 

 vacuum bubbles in fluid inclusions in considerable 

 quantity. 



Last year a note on datholite as occurring in the Cole- 

 brook limurite was submitted by one of us to the society, (f) 

 and we hav-e since taken occasion to examine this mineral 

 microscopically. In thin section it is colourless, but in 

 polarised light the interference colours are high, comprising 

 the tints of the second and third orders of Newton's scale.. 

 The doulile refraction is slightly under that of augite. In 



* Massige Gesteine. H. Rosenbusch, 1896, p. 103. 



t Notes on some recently discovered and other minerals occurring iu. 

 Tasmania. W. F. Petterd. Proc. Roy. Soc. Tasm. 1897, p. 63. 



