34 



An analysis of the dolerite, for which I am indebted to 

 Mr. H. YatoS', B.S'C, is given in column i. below: — 





I. 



II. 



SiO^ 



... 49-32 



49-29 



Al,03 ... 



... 21-03 



18-81 



Fe,03 ... 



... 1-79 



3-57 



FeO 



... 8-31 



7-78 



MgO ... 



... 2-31 



3-28 



CaO 



... 10-91 



9-25 



Na^O ... 



... 2-97 



3-07 



K,Q 



0-47 



2-10 



H3O+ ... 



... 0-63 



1-07 



H3O- ... 



... 0-10 



0-20 



CO, 



abs. 



tr. 



TiO, 



... 1-96 



2-17 



PA ••• 



... 0-12 







s • 



... p.n.d. 



— 



Total 99-92 100*59 



Sp. gr. at 15 °C 2*992 



I. Uralitic dolerite, dyke at back of Rosetta Head. 

 Anal. H. Yates. 



II. Olivine diabase, west side of .Blinman Mine. Anal. 

 W. N. Benson. Trans. Boy. Soc. S. Austr., vol. 

 xxxiii., 1909, p. 234. 



Perhaps the most noteworthy feature of the analysis is 

 the low magnesia. A careful check determination failed to 

 increase the figures, so they may be accepted as correct. 



On a rough estimate, based on the examination of a thin 

 section, the rock contains between 60 and 70 per cent, of 

 amphibole and less than 30 per cent, of plagioclase. 

 This great predominance of amphibole shows that much of 

 the lime and alumina of the analysis must be contained 

 in this mineral, which, therefore, cannot be regarded as 

 true actinolite. With the exception of the potash percentage 

 the analysis of this rock corresponds very closely with that of 

 the Blinman diabase. 



The question naturally arises as to why these dolerites 

 have been so completely uralitized, seeing that the granitic 

 rocks, of earlier intrusion, have remained unaltered. It seems 

 evident that no external agency was at work to produce the 

 change, and one must conclude, following Duparc and 

 Hornung,(25) that the uralitization has been of the nature of 



(25) Comptes Reiidus, vol. 139, 1904, p. 223. Quoted by J. A. 

 Thomson, W. Aiistr. Gool. Surv. Bull. 33, p. 132. 



