PROCEEDINGS OF SECTION C. 189 



2.— ON THE COMPOSITION AND ORIGIN OF AUSTRALITES. 



By H. S. Summers, M.Sc, Lecturer and Demonstrator in Geology, 

 University of Melbourne. 



Plate VII. 



Introduction. 



Ever since the first record by Charles Darwin* in 1851, interest 

 has been maintained in the occurrence and origin of the bodies variously 

 known as Obsidian Bombs, Obsidian Buttons, Obsidianites, Australites, 

 &c. 



In the earlier days they were generally referred to as Obsidian 

 Bombs or Obsidian Buttons, but latterly the name Obsidianite has 

 been in more general use. In 1900 Professor Suessf suggested the 

 name Australite, and this name seems to be the most suitable. In the 

 first place it has been shown that the composition of these bodies 

 differs from that of true obsidian, and in the second place the name 

 Australite is more in accord with the names applied to somewhat similar 

 substances found elsewhere, i.e., "Moldavites" from Moldau River, 

 " Billitonite " from the Island of Billiton, and " Australites " from 

 Australia. These three types have been grouped together by Suess 

 under the name " Tektites." 



During the latter part of 1912 Mr. E. J. DunnJ published an elabo- 

 ration of his " bubble hypotheses " to account for the origin of Aus- 

 tralites, and one purpose of this paper is to answer certain criticisms by 

 Mr. Dunn on a previous paper read by me before the Royal Society 

 of Victoria. § At the same time, attention must be called to two other 

 hypotheses which have been recently advanced to account for the 

 origin of Australites. Professor E. P. Merrill, || believes that Australites 

 represent rolled Obsidian pebbles, while Professor J. W. Gregory^! 

 suggests that they may habe been formed by the fusing of atmospheric 

 dust by lightning discharge. 



Composition of Australites. 



Since the publication of my earlier paper** on this subject, two 

 additional analyses of Australites have been made, and these are set 

 out below. 



* Q3ological ob33rvatioa3 on Coral B3efs, Volcanic Islands, and in South America, 1851. 

 Reprint 1890. pp. 190-191. 



t Jahr d.k.k. Geol. Beichsanst, Vienna. Vol. 50, 1900, p. 194. 



t Bull, of the Geol. Surv. of Vic. No. 27. 1912. 



§ Proc. Roy. Soc. Vic. Vol. XXI (N.S.), Pt. II, 1908., p. 423. 



i| Proc. U.S. Nat. Museum. Vol. XI, 1911, p. 481. 



H The Making of ths Earth (Homs University Series), p. 36. 



•* Op. eit. 



