434 



H. S. Swimei'f^ : 



I. — Obsidianite from near Coolgardie, Western Australia. 



II. — Obsidian from Mayer's Island, New Zealand. Analysed 

 by P. G. W. Bayly. — Records of the Geol. Survey of Victoria, 

 Vol. II., Part 4, 1908, p. 205. 



III. — Andesitic Pumice from Krakatoa Eruption, 1883. An- 

 alysed by C. Winkler. Washington, Chemical Analyses of 

 Igneous Rocks, p. 193. 



IV.— Phonolitic Trachyte from top of 900 ft. knoll. Mt. 

 Terror, South Victoria Land. National Antarctic Expedition, 

 1901-1901. Natural History, Vol I., Geology, pp. 114, 119. 



The norms corresponding to these analyses are : — 



From these results we obtain the following classification : 



The analysis of the New Zealand obsidian is that of a fairly 

 normal acid glass, in which the sum of the alkalis very greatly 

 exceeds the lime. Other analyses of New Zealand rhyolitic 

 rocks quoted by W^ashington are found to be closely related to 

 that of the Mayer Is. specimen. 



