Notes on Obsidian and Avstralites. 83P 



In the American classification ])oth rocks belong to — 

 Class 2. Dosalane. 

 Oi-der 4. Dofelic. 

 Rang 2. Domalkalic. 

 Sug-Rang 3. Sodipotassic. 

 Their inagmatic name is Adamellose. 



This comparison shows that in chemical composition the Taradale 

 rock belongs to the basic end of the intermediate class, while the 

 mineral phenocrysts and apjiarently its field occurrence suggest a 

 genetic relationship with the basalts. It is quite clear that rlie 

 rock is not obsidian. 



This analysis of the evidence of the so-called obsidian from 

 Geelong and from Taradale shows that Mr. Dunn's claim that 

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

 exists in Victoria associated with the newer volcanic rocks, is 

 quite unwarranted by the evidence so far available. 



The chemical characters of austral ites. 



The literature ou australites, obsidianites, or obsidian buttons as 

 they wei-e formerly called, is now voluminous. The best papers 

 describing the physical characters of these bodies are Mr. Walcott'si 

 and Mr. Dunn's. 2 



The illustrations in Mr. Dunn's paper are particularh" valuable. 

 From the point of view of origin and chemical relationships the 

 most important papers are by Dr. Summers^ and Dr. Suess."* Dr. 

 Summers has given the most complete discussion of their origin from 

 a chemical standpoint, and has given a fairly complete bibliography 

 of the literature, which it is unnecessary for me to repeat. 



Among the hypotheses as to the origin of australites are the 

 following : — 



1. That they are artificial bodies. 



2. That they have been formed by lightning discharge during 



dust storms. 



3. That they are of volcanic origin. 



4. That they are of meteor itic origin. 



For the first two hypotheses no serious evidence or arguments 

 have been advanced. 



1. Walcott. Proc. Roy. Soc. Victoria, vol. xL, (ii.s.), 1898. 



2. Dunn. Records CJeol. Surv. Victoria, vol. ii., pt. iv., IWS. Bulletin Geol. Surv. Vict., 

 No. 27, 1912. 



3. Summers. Proc. Roy. Soc. Victoria, vol. xxi. (n.s.), pt. ii., 1909: Aust. Assoc. Adv. Sc, 

 Melb., 1913. 



4. Suess. Jahr. d. k.k. Geol Leichaust. Vienna, vol. 50, 1900, p. 194. 



