41 



glass which surrounds thein (1 and T488). Some large 

 circular gas pores are seen in the section surrounded bj glo- 

 bulites and yellow glass. Here and there aggregations of 

 globulites occur, associated with yellow or brown glass. 

 Glass inclusions are also present. Obsidian from the Thames 

 district, New Zealand (sp. gr. 2-41), has the same globulitic 

 devitrification, but is sprinkled with belonites and forked 

 inicrolites. The Hungarian and Mexican obsidians are crowded 

 with crystallitic and microlitic forms, and, judging from our 

 slides, are not comparable either with the New Zealand or the 

 Tasmanian obsidian. 



The purest natural glass in the world is perhaps fulgurite 

 glass, which is supposed to have been produced by the fusion 

 of rock by lightning. This structureless glass contains no 

 crystallisation products whatever, and contains nothing 

 beyond glass enclosures aud gas vesicles*. The Tas- 

 manian obsidian does not attain this degree of purity, but 

 approaches to some extent the clearness of bouteillenstein, 

 which is a remarkably pellucid natural glass. The buttons 

 under review must not be classed with the bombs which are 

 ejected from modern volcanoes in New Zealand. The latter 

 are of an entirely different nature, for they belong to the 

 basic division of eruptive rocks. They are somewhat cylindrical 

 in shape, of a dark grey colour, externally scoriaceous, with 

 the internal texture of a compact lava. A section which we 

 have made of a bomb ejected from Rotorua shows it to be 

 an olivine-basalt lava, containing phenocrysts of olivine, 

 (invaded and corroded by the magma) and augite in a glassy 

 base in which microliths of felspar and augite have crystal- 

 lised. In accord with these basic features, we find its specific 

 gravity to be 2737. 



The strange feature of the Tasmanian occurrence is that no 

 glass of similar igneous rocks is known in the island, nor 

 any trace whatever of tertiary or recent rhyolites or trachytes. 

 The specimen from Thomas Plains which we figure was 

 found in the old Union claim near Weldborough in 1875 

 below the surface soil, about 5 or 6ft. deep, in the clay which 

 caps the stanniferous quartz drift. In all, three examples 

 were obtained in comparatively close proximity to each 

 other. A few years later another was obtained from a heap 

 of tailings on Thomas Plains,, only two or three miles from 

 those just mentioned. 



Mr. John Cherry, of Springfield, in reply to our inquiry, 

 informs us that he found a button in a bed of quartz wash 

 six inches thick, overlaid by two feet of alluvium, the whole 

 resting upon granite. He found a second specimen about 

 a mile from the first, lying on the surface of the ground. 



* On Fulgurite from Mt. Blanc : F. Rutley, Q. J. Geol. Soc. Vol. xli., 1885, p. 152. 



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