PROCEEDINGS OP SECTION C. 19$ 



table (i.e., Nos. 1, 2, 3, 6, 9, 10, 11, 13, 17 of the preceding table of 

 analyses), all conform fairly closely to curves. 



Even accepting all the analyses as being correct, the curves are 

 suflSciently good to indicate a genetic relationship between the Aua- 

 tralites, Biljitonites, and Moldavites. Were the analyses quoted above 

 those of rocks of terrestrial origin one would conclude that they belonged 

 to a common petrographic province, as the variation from the mean 

 position is less than that frequently met with in plotting analyses of 

 rocks of known community of origin. The inference then is that the 

 tektites, i.e., Australite, Billitouite, and Moldavite, are derived from a 

 common source, whether that source be terrestrial or extra-terrestrial. 



It is strange that Mr. Dunn should endeavour to disprove the 

 genetic relationship of Australites, for in so doing he is advancing an 

 argument against his own hypothesis. Mr. Dunn states that all the con- 

 ditions necessary for the production of his bubbles appear to be present 

 in volcanoes. No such bubbles have been observed, so we naturally 

 presume that in the case of present-day volcanoes the necessary con- 

 ditions are not present. No bodies of similar form to Australites have 

 been recorded from other parts of the world, and this, together with 

 their non-formation in existing volcanoes, renders it certain that if 

 their production did take place in the past it was quite an abnormal 

 occurrence. Consequently, we would expect that the blowing of such 

 bubbles would be confined to one volcano or group of volcanoes, and 

 that the blebs would show a genetic relationship with one another. 



Form. 



One of the most interesting problems about Australites is the form 

 that they have assumed. In Mr. Dunn's paper is an exceptionally 

 valuable collection of illustrations of these bodies, and all the various 

 types are well sho^vn. 



Two explanations have been put forward to account for the form : — 



(a) They formed the blebs of bubbles blown in the throat of a 



volcano. 

 (6) The form was assumed during their flight through the air 



owing to rapid rotation while in a molten condition. 



The first hypothesis, due to Mr. Dunn, seems to have nothing to 

 support it, and a few of the objections are given below : — 



1. An examination of the button forms having a complete rim 

 shows that in general the edge is smoothly rounded and 

 that there is a complete absence of any sign of the sup- 

 posititious fracture due to the breaking away of the 

 hypothetical bubble. 



6117. G 



