NoteK o)i Obsididn and Anntrdlitcti. 385 



The so called obsidians from Geelong. 



In the Notes on the Physical Geography, Geology and Mineralogy 

 of Victoria, by A. H. Selwyn and G. H. F. Ulrich, published in. the 

 Intercolonial Exhibition Essays, 1866, p. 65, obsidian is stated 

 to occur in a basalt quarry near Geelong in patches and irregular 

 veins of an inch or more in thickness. Two analyses by Mr. Cosmo' 

 Newbery are quoted from this locality. The same statements and 

 analyses are quoted in Selwyn's Descriptive Catalogue of the rock 

 specimens and minerals in the National Museum, collected by the 

 Geological Survey of Victoria, 1868, p. 80. The specimens are 

 labelled Specimen 24 and 24a. 



These are two of the analyses quoted by Mr. Dunn, and are a& 

 follow : — 



101.01 98.34 



To anyone accustomed to rock analyses the above figures at once 

 suggest inaccuracy, not only by the summation, but still more by 

 the curious and unusual proportions of some of the oxides. 



Mr. Dunn has overlooked the fact that as long ago as 1898 Mr. 

 Walcotti in his paper on Obsidianites had examined these speci- 

 mens, had called attention to the discrepancy between the published 

 analyses and the appearances of the specimens and had detached 

 a chip from specimen 24 and by chemical analysis obtained only 

 53.2 per cent, of silica. He pointed out that the appearance and 

 silica percentage pointed to the mate'-ial being tachylyte and not 

 obsidian. 



1 Proc. Roy. Soc. Victoria, vol. xi. (N.S.), 1898, p. 32. 



