52 PROCEEDINGS OP THE WASHINGTON MEETING 



Australian and other geologists. Numerous analyses and a valuable discus- 

 sion of the origin of these bodies will be found in a paper by H. S. Summers, 2 

 and an excellent set of figures accompanying a discussion of the genesis has 

 been published by E. J. Dunn, 3 former Director of the Geological Survey of 

 Victoria, Australia. In these publications various references to the bibliog- 

 raphy on this subject will also be found. 



Characteristics and Origin 



The australites are small bodies of glass, often of remarkably perfect form, 

 so perfect in some cases as to suggest an artificial origin. They are sometimes 

 button-shaped, sometimes dumb-bell in shape, sometimes spherical, and at 

 other times quite irregular in form. Many of them show flow structures and 

 often pitted surfaces are developed. In chemical composition they are much 

 like obsidian, although they are peculiar, in having in most cases a higher 

 lime and magnesia content in proportion to potash and soda than is generally 

 found in rocks so high in silica and in which the potash is usually higher than 

 the soda. Summers, therefore, endeavors to show that they do not correspond 

 to any terrestrial rock type. They are undoubtedly related to one another in 

 chemical composition, as he points out, and most of them can doubtless be 

 regarded as having a common source, yet comparison of the analyses with 

 other special types show a close resemblance to some types of obsidian. 



There have been advanced several theories to account for the origin of these 

 peculiar bodies, the two main theories being the volcanic and the meteoric. 

 The greatest difficulty so far confronting the volcanic theory is the distribu- 

 tion of the australites, which occur over a band stretching across Tasmania 

 and over the whole of the southern part of Australia from the east to the west, 

 covering the greater part of the island south of the tropic of Capricorn. Vari- 

 ous suggestions have been made to account for their transportation, amortg 

 them Mr. Dunn's ingenious bubble hypothesis, transportation by aborigines, 

 emus, etcetera. These means have never appeared entirely satisfactory be-' 

 cause, as pointed out by Summers, the australites are believed to be of Cenozoic 

 age — although I believe they have never been found embedded in any solid 

 formations — and that while there may be known volcanoes of this age in Vic- 

 toria, some of the specimens are still found at least 2,000 miles from these 

 volcanoes, and so far no deposits of obsidian have been found connected with 

 them. 



To account for the distribution, therefore, the meteoric hypothesis has been 

 advanced, but this is open to as great objections as the other. In the first 

 place, the composition, form, and internal structure of the bodies are quite 

 different from those of known meteorites, and in the second place it seems 

 hard to realize how such perfectly formed bodies, which give every indication 

 of having been in a liquid condition, could strike the earth from some extra- 

 terrestrial source and have their outline so well preserved. If the heat which 

 caused them to become liquid were due to atmospheric friction, it would be 



2 H. S. Summers : Obsidianites — their origin from a chemical standpoint. Royal Soc. 

 of Victoria, vol. xxi (new series), 1909. 



H. S. Summers : On the composition and origin of australites. Report of the Aus- 

 tralian Association for the Adv. of Sci., vol. xiv, 1913, pp. 189-199. 



3 E. J. Dunn : Australites. Bull. No. 27, Geol. Survey of Victoria, 1912. 



