Notes on Ohsidid/)! and Auslialites. 341 



The Uralla australite while quite extreme in iheinical composition 

 is shoAvn by Dr. Summers to lie on a curve containing most of the 

 australites which have been analysed. In the case of the Taradale 

 rock the points for ferrous oxide, soda and total alkalies lie a long 

 way outside the main curve of most of the australites. 



The comparison of the two types by both methods, therefore, in- 

 dicates their essential dissimilarity and the dissimilarity between 

 the Taradale rock and australites in general. 



Incidentally it may be noted that Mr. Dunn's comparison of the 

 Taradale rock is not with Victorian australites, as one would 

 expect, but with a New South Wales australite of quite extreme 

 composition. This is curious since Mr. Dunn's claim is to establish 

 a connection between australites and Victorian volcanic rocks. Of 

 course a comparison with analyses of Victorian australites would 

 have at once shown an almost complete dissimilarity of composition. 



The complete failure up to the present of all attempts to locate 

 any newer volcanic rocks in Victoria, or even in Australasia, which 

 are similar in chemical composition to the australites, is a for- 

 midable difficulty in the way of the acceptance of a volcanic origin 

 for these bodies. With the large and rapid increase of our know- 

 ledge of the newer volcanic rocks of Australasia, made in recent 

 years, the probability of finding rocks of such peculiar composition 

 becomes less and less, and the argument, though based on negative 

 evidence, that the australites are not of volcanic origin has been 

 proportionately strengthened. 



Even if. a volcanic rock of similar composition to that of the aus- 

 tralites were found in Australia, the difficulties of the distribution 

 of these bodies, in many cases hundreds of miles from any volcanic 

 rocks, remains as has been pointed out by Dr. Summers. The 

 shapes of these bodies, and especially the smooth nature of the 

 flange, appear to me to negative Mr. Dunn's ingenious hypothesis 

 that they represent the blebs of volcanic bubbles, a hypothesis put 

 forward by Mr. Dunn to explain not only their form, but also 

 their distribution. 



It is the general failure of the volcanic hypothesis rather than 

 positive evidence in favour of an extra-terrestrial origin which 

 leads most modern writers on this subject to regard the meteoritic 

 hypothesis of the origin of australites as the most probable one in 

 view of the present state of our knowledge on the subject. 



