Obsidian Bombs in Australia. 49 



highly probable that in substances of their composition the 

 shapes would be produced after entry into the earth's atmo- 

 sphere, and that they represent fragments of comparatively large 

 bodies. The enormous sudden temperature which would be 

 generated on impact with the atmosphere would be almost 

 certain to cause the original body to burst, resulting, in all 

 probability, in an almost complete shattering of the body, and 

 also probably complete consumption of the greater portion of it. 

 Under these conditions the astonishing thing is, if they are 

 meteoric, that they should have reached the earth's surface at all. 

 Whether these bodies were originally glassy we cannot surmise, 

 because, as they have been molten throughout, they may have 

 resulted from the melting and rapid cooling of crystallised masses. 

 The supposition of a molten state is certainly an unusual one 

 amongst meteorites, as they bear strong evidence of only having 

 been molten to an insignificant thickness of their surface, 

 although there are instances in which some meteoric stones, or 

 aerolites, appear to have been heated throughout their mass to a 

 high temperature. 



If, after the bursting of the original body, the various fragments 

 were in a plastic condition, the shapes might have been induced 

 by the hurling of these fragments through the air in all directions 

 with different degrees of velocity. The time it would take these 

 objects to reach the earth's surface would be extremely small, 

 perhaps only a few seconds, and it might be expected that they 

 would then be in at least a soft state. If this were so it would 

 surely show itself by a flattening or otherwise in altering the 

 original symmetrical form, but, as previously mentioned, in those 

 examined there is no appearance whatever that such is the case. 

 We must then believe that they cooled down with great rapidity, 

 an operation which would have produced an extreme brittleness 

 in a glassy substance — so much so, that a fall on the earth would 

 have completely shattered them. Contrary to this expectation, 

 they exhibit even less brittleness than obsidian from lava flows, 

 which exists in masses and under conditions much more favour- 

 able to a slower rate of cooling. Nevertheless, it is most likely 

 that only those survived that fell under favourable conditions 

 and that many others were destroyed on contact with the earth 

 whether of cosmic or terrestrial origin. With regard to their 



