56 



substance, 0*6 inch in diameter, having a specific gravity of 

 2*7 al a temperature of 66 degrees. It was undivided, and 

 more like those examples described by M. Beudaut than the 

 figure given by Mr. Darwin. A similar specimeu, but of a 

 rude elliptical form, half an inch in diameter in the major 

 axis, and having a specific gravity of 2-57 at a temperature 

 of 63 degrees, was iouud in the washing stuff of the Uralla, 

 or Rocky River. 



"From the same locality were derived two other specimens, 

 which I have examined. These are perfectly round, having 

 diameters respectively, including the rim, of liulf an inch and 

 about three-quarters of an inch. These, except in the shape 

 and in the extension of the cells over the rim, as well as in the 

 nucleus, agree with Mr. Darwin's figure. Their colour is 

 also bottle-green, and they are translucent, the surface 

 appearing black, as in Mr. Darwin's specimen. But this 

 blackness does not arise from any difference in the composi- 

 tion. It is merely the effect of greater opacity. The external 

 concentric rings are evident in all three. The specific gravity 

 of those from the Uralla is respectively 242 and 2*51, at a 

 temperature of 63 degrees. The smaller very much re- 

 sembles a button without the shank, and from this appear- 

 ance the diggers call them ' button-stones.' They appear 

 as if they had been cast in a mould, but there is no reason 

 to doubt the imputed origin." 



The latter part of Mr. Clarke's description clearly identifies 

 the Uralla specimens with those described by Messrs. Twelve- 

 trees and Petterd. The high specific gravity of the Turon 

 specimen places it with basalt-glass rather than true obsidian. 



Mr. Clarke states that the alluvium of the Uralla is in. 

 granite country, but that a plateau in which the river rises 

 has ranges which are created by basalt, and he infers " that 

 the bombs had their origin in the outburst of the trap." 



In the following year, Mr. Clarke reportsf the discovery 

 of two additional specimens. One of them was found at the 

 Supply Rivulet, River Tamar, Tasmania, by Dr. Milligan. 

 The other, " like a bung in shape, an inch high, and 1^ of 

 an inch thick in the upper part," was found near the River 

 Wannon, in Victoria. No other particulars are given. 



Mr. G-. H. F. Ulrich, now Professor in the University of 

 Dunedin, while connected with the geological survey of 

 Victoria, prepared for the Melbourne International Exhibition 

 of 1866, a paper on " The Mineral Species of Victoria/' from 

 which the following remarks on obsidian are quoted : — 



" Button-shaped and spheroidal pieces of this mineral, from 

 a quarter of an inch to several inches in diameter — the larger 



+ " Additional Notice of the Occurrence of Volcanic Bombs in Australasia. By 

 the Rev. W. B. Clarke, M.A., F.G.S. (Abstract)." Quarterly Journal of the 

 Geological Society, December, 1856. 



