24 
C. G. THORP, M.B., C.M. : 
Australites show so little flow structure in their central mass, or 
at most just a smooth circular flow, but as in the button form 
demonstrated by Mr. Dunn in his last paper on the subject any 
violent whirls are confined almost entirely to that easily detach- 
able outer ring, which is not represented in our conical form. 
This hypothesis can only be absolutely proved by seeing 
the process actually at work, and finding on the spot bubbles, or 
at least broken bubbles with blebs that have for some reason 
failed to be caught by the air current that would carry them 
away. 
It will, in my opinion, be found that Billitonites are, some of 
them, these failures, as they may be called ; some, as 1 say, 
from missing the sufficient upward blast and some from the 
clumsiness of deformity, while others are really Australites 
which have chanced to go north instead of coming south (Plate 
XXI, Figs. I to 4). It may, I think, be said that the bubble 
portion of the problem is more than half answered by the existence 
of the hollow specimens to which reference will be made later 
(Plate XVIII, Figs, x and 2). 
The problems at present requiring special research, apart 
from the exploration for the actual volcano, are physical and 
mathematical. Physical, to work out the properties of the glass 
of which these bodies are formed, and to learn by actual experi- 
ment the possibility or impossibility of forming bubbles of thfs 
material sufficiently thin, yet rigid” enough when filled with a 
light gas, to float in rarified air, or rather to sink slowly in this 
medium. To learn the mode of formation of the dumb-bell, 
long narrow and other aberrant forms, whether they are caused 
by the junction of two bubbles which afterwards unite entirely 
without a septum or from two or more blebs on one bubble which 
have run together and united. Many of the irregular forms are, 
without any doubt, caused by the breaking, chipping and sand 
wearing of the regular normal shapes. Mathematical, to deter- 
mine whether, in the event of bubbles being formed by natural 
means and thrown with sufficient force into the air to reach the 
distributing wind, they could remain suspended long enough to 
allow them to be carried to the localities where they are now 
found. Much accurate data, also requiring- research, would be 
necessary to get reliable results. 
At the very commencement of my first introduction to these 
most interesting bodies I was so fortunate as to be able to examine 
a very large collection of them. The peculiarity noticed at once, 
and that struck me most particularly, was the curiously few 
patterns produced and the almost mathematical exactness 
exhibited in their production. This latter is one of the most 
remarkable things of which I know, these few definite patterns 
