[Proc. lioY. Soc. Victoria, 27 (N.S.), Part \I., 1914]. 



Akt. ^XW.—Nofe.^ on the s()-(;aUed Obsidian ffoni Geelong and 

 fr<n)i Taradale, and. on A'iistndites. 



By Profkssok K.RNE.ST W. SKEAT8, D.Sc, A.R.C.S., F.G.S. 

 L^ead lOtli December, 1911]. 



Introduction, 



In the Records of the Geological Survey of Victoria, Vol. III., 

 Part 3, 19U. pp. 322-326, recently published, Mr. E. J. Dunn. 

 F.G.S. , in a paper entitled " Further notes on Australites," quotes 

 some old analyses of Mr. Cosmo Newbery of two specimens of 

 "obsidian'' from the Geelong district, of a "basalt'' from neai- 

 Kyneton, and of an australite from the Wimmera Plains. In 

 addition a recent analysis of a so-called obsidian from Taradale 

 is quoted, and the claim is made in the paper that these analyses 

 show that acidic volcanic glass, similar in composition to that of 

 australites exists in Victoria associated with the newer volcanic 

 rocks. 



Mr. Dunn's long and wide experience as a field geologist ensures 

 that any paper of his dealing witli problems of field geology will 

 command confidence and respect fi'om all geologists. He has had, 

 however, no special experience in chemical and jDetrological ques- 

 tions, and the problems raised in his recent paper and on austral- 

 ites generally are to a large extent chemical and petrological. In 

 consequence of this I feel that he has misunderstood tlie evidence 

 and come to erroneous conclusions. 



The object of this communication is to criticise some of tlie 

 evidence stated in Mr. Dunn's paper and to show that the older 

 rock analyses of the Geological Survey of Victoria, in common with 

 many old rock analyses, arc quite unreliable, tliat tlie rocks from 

 Geelong, described as obsidian, are ically tacliylytv. that the 

 rock from Taradale is not obsidian, l)ut ii vok-anic glass of peculiar 

 composition and belonging to the Intei'inediate division, that no 

 rock of the nature of obsidian is known to occur among the newer 

 Volcanic rocks of Victoria, and that in consequence no support is 

 lent to the hypothesis of the volcanic oiigin of australites by an 

 appeal to the chemical composition of the newer volcanic rocks of 

 this State. 



