■674 dr. j. a. tucoison ox the [Dec. 1913, 



this statement, for they show that the araphibolites (within the 

 Kalgoorlie area proper) rarely contain more than 50 per cent, of 

 silica, the actual figures being 46-26, 46-38, 4742, 48-86, 49-06, 

 and 50- 72. 1 Now, it may be unhesitatingly asserted that the 

 average silica-percentage of quartz-dolerites exceeds 50; and, since 

 tbe greenstones contain, on the whole, more micropegmatite than 

 an average quartz-dolerite, and more than the amphibolites, the 

 original silica-percentage of the rocks from which they were 

 •derived must have exceeded 51 and may have approached 54. 

 This phenomenon of the alteration selecting the most acid part of 

 the intrusion has a parallel in the case of the juvenile albitization 

 •described by Bailey & Grabham, and certainly makes it probable 

 that the mode of alteration was in each case similar. 



As I have already stated in the body of this paper, there are 

 ■certain epidotic greenstones in the ' North End ' that give colour to 

 Mr. Simpson's view. A full discussion of the subject would involve 

 a long digression on the problem of uralitization, on which very 

 •contradictory opinions have been expressed in recent works, and 

 such a discussion would be out of place here. It is, in my view, 

 quite conceivable that the later carbonating solutions, which found 

 the peridotites already altered to serpentines, may have found the 

 more basic part of the quartz-dolerites already converted into 

 amphibolites, and may have further altered these into epidotic 

 greenstones. Another alternative mode of origin of these green- 

 stones, equally in conformity with the theory of juvenile albitization, 

 is that in the North End the albitization and accompanying 

 changes were only partial, and that subsequently uralitization and 

 saussuritization affected those parts of tbe original pyroxenes and 

 lime-soda felspars that were left intact. Obviously, the problems 

 in Kalgoorlie are very complex, and, despite the large amount of 

 study that they have received in recent years, there is still much 

 left for the petrologist to unravel. 



VII. Bibliography. 



'C. J. Alford. — 'Gold in Western Australia' Mining Journ. vol. lxvi (1896) 



p. 911. 

 • G. J. Bancroft. — ' Kalgoorlie (Western Australia) & its Surroundings ' Trans. Am. 



Inst. M. E. vol. xxviii (1898) pp. 88-100. (For Discussion, see E. S. Simpson, 



ibid. p. 808.) 

 H. Y. L. Brown. — ' Report on the Nature of the Auriferous Deposits of Western 



Australia' South Australian Parliamentary Paper, No. 26, 1896. 

 G. W. Card. — ' Report on some West Australian Rocks ' Ann. Rep. Dep. Mines, 



N.S.W., for the Year 1897. Sydney, 1898, p. 192. 

 . ' Notes on the Country Rock of the Kalsioorlie Goldfield ' Rec. Geol. Surv. 



N.S.W. vol. vi, pt. 1 (1898) pp. 17-42 & pis. i-iii. 

 A. Carnot. — ' Sur les Tellurures d'Or & d' Argent de la Region de Kalgoorlie 



(Australie Occidentale) ' Bull. Soc. Franc. Min. vol. xxiv (1901) pp. 357-67, 



and C.R. Acad. Sci. Paris, vol. cxxxii (1901) pp. 1298-1302. 

 C. Chewings. — ' Geological Notes on the Coolgardie Goldfields ' Proc. Roy. 



Colonial Inst. vol. xxvii (1896) pp. 215-71. 



1 These amphibolites are not all derived from quartz-dolerites, the first 

 (Si0 2 = 46-26, MgO=19 65, CaO = <r94, being certainly a lustre-mottled 

 amphibolite 



