43 



somewhat broad median band, which is irregularly finely 

 indented. The outer margin of one face has a row of 

 extremely minute crenulations which are almost microscopic. 

 This is the only specimen which has come under our notice 

 of the Australian type, as it is without the flange or beading, 

 which is apparently characteristic of the buttons obtained on 

 the East Coast. 



The Australian bombs have been compared with the 

 nodules of bouteillenstein (pseudo - chrysolite, moldavite) 

 translucent to brown in colour, found in sand near 

 Moldanthein in Bohemia, and in tuff in the Auvergne, 

 as well as with the glassy marekanite balls of the Mai'ekanka, 

 near Okhotsk, in Eastern Siberia. But the nature of mare- 

 kanite is now well understood. It is the perlitic or sub- 

 pumiceous modification of a glassy rhyolitic rock in situ on 

 the Marekauka, the concentric jointing of which detaches 

 onion-like spheroids. The nuclei of these spheroids are the 

 marekanite glass balls, which vary in size from that of a pea 

 to that of an orange. In his paper on marekanite, Professor 

 Judd* refers to the description by Damour, in 1844, of a 

 black obsidian ball from India, 2|in. diameter. This ball 

 had the composition of dacite glass (sp. gr. 2"47), but unfor- 

 tunately its locality was not known. 



The nodules of bouteillenstein are undoubtedly obsidian, 

 but the localities in which they are found do not suggest any 

 serious difficulty in accounting for their presence, though no 

 detailed comparison appears to have been instituted between 

 their nature and that of the rocks belonging to the adjacent 

 volcanic centres. In Australia and Tasmania, volcanic rocks 

 are either absent from the vicinity, or belong to quite a 

 different penological family, aud consequently could not have 

 been a source 



Mr. Verbeek records similar obsidian balls from the quar- 

 ternary, or perhaps pliocene tin ore deposits of Billiton; from 

 quarternary tuff strata in Java, and from gold and platinum 

 mines of the same age in South Eastern Borneof. We 

 may here draw attention to the circumstance that all over 

 the wide area of the earth's surface in which these bombs occur, 

 they are found only in deposits of the later tertiary or the 

 recent period. 



Analyses of some of the Victorian specimens were made 

 by Mr. Cosmo Newbery, and published in the " Descriptive 

 Catalogue of the Rock Specimens and Minerals in the 

 National Museum, 1868." Bv the courtesv of Mr. B. H. 

 Walcott, we are able to give the particulars of one of these 

 analyses, and we append, for comparison, Cohen's analysis of a 



* On Marekanite and its allies. Prof. J. W. Judtl, Geol. Mag., 1886, p. 245. 

 t " Nature," May 13, 1897. 



