606 MINERALS AND VEINS pF JEGIRINE-SYEN1TE, 



The unique feature amongst the minerals is the abundance of 

 a secondary amphibole usually resembling the primary arfved- 

 sonite, but occasionally near crocidolite and riebeckite; this 

 appears to be the first record of uralitisation (typically shown) 

 of segirine to form alkali-amphibole.* The reverse process, an 

 extraordinary proceeding not elsewhere noted in the case of any 

 of the pyroxenes, has been described by Brogger as taking place 

 in the pegmatite dykes of Christiania. 



The uralitisation succeeded consolidation, and proceeded under 

 hydrothermal conditions very active in corroding the felspars 

 and to some extent the quartz; as the secondary minerals contain 

 scattered grains of fluorspar and are largely carbonates, it is 

 inferred that the metachemisation was effected by circulating 

 solutions rendered highly active by containing a small amount of 

 fluorine and large quantities of alkali carbonates. 



Pegmatites of the segirine-syenite following have not, so far as 

 I am aware, been previously described, and might well be called 

 Bowralite — a coarse-textured holocry stall ine type composed 

 essentially of idiomorphic sanidine, subordinate alkali-amphibole 

 typically arf vedsonite, and some segirine. See the hand-specimen 

 photograph, Plate 1., fig."2. 



Conclusion. 



The work herein contained was begun at the Sydney University, 

 and I am indebted to Professor T. W. E. David, F.R.S., etc., and 

 H. S. Jevons, M.A., for suggestions on the petrological side; and 

 to Professor A. Liversidge, F.R.S., etc., and J. S. Schofield, 

 A. R.S.M., for assistance in analysis. Much of the analytical 

 work had to be repeated, later, here in Adelaide, and for its 

 consummation my best thanks are due to Professor Rennie, D.Sc, 

 for unstinted liberality in the matter of apparatus and con- 

 veniences, often attended with personal discomfort to himself. 



* Cross and others have described cases of secondary regirite on amphibole 

 and vice versa, but such probably do not actually indicate uralitisation. 



