39 



ON THE OCCURRENCE OE OBSIDIAN "BUTTONS 



IN TASMANIA. 



Read August 2, 1897. 



By W. H. Twelvetrees, F.G.S., & W. F. Petterd, C.M.Z.S. 



The little grooved aud rounded discs of lava known as 

 obsidian buttons (and among local miners as fossil gum 

 seeds [eucalyptus] or pods) found occasionally in the tin 

 drift at Thomas Plains, Eastern Tasmania, and at Long 

 Plain, near Waratah, have not attracted much attention 

 hitherto, but are now acquiring particular interest from 

 European researches in connection with similar occurrences 

 •elsewhere. They are by no means plentiful, and only eight 

 specimens have come into our hands ; six from Thomas 

 .Plains : one from Mr. Cherry's property at Springfield, near 

 Scottsdale ; and another from Long Plain. Their occurrence 

 has been recorded in the work cited below.* They are 

 generally nearly hemispherical in shape, with a few concentric 

 rings or flutings round the hemisphere. The edge of the 

 disc is smoothly irregular, with distant sub-depressions. The 

 flattened side or base is slightly concave, with a central 

 convex elevation, which is ringed round with a distinct 

 beading. In colour they are intense black, somewhat dull 

 from a thin epidermal skin. The merest fracture, 

 which is conchoidal, shows a lustrous glass beneath. On 

 their edges the colour becomes deep grey to yellowish 

 brown, and the glass translucent. They are somewhat 

 constant in size, both as regards diameter and thickness, the 

 largest measuring l|in. in diameter by fin. in height. 



There are only two exceptional forms which we have seen 

 or heard of, viz., one which has been likened to the outline of 

 the elytra of a large beetle, which is shown by a specimen in 

 the possession of Mr. Aug. Simson, and another of a more 

 elongated form. In the first of these, the general pattern of 

 its grooves, beading, and wrinkles is similar to that of the 

 others ; and it is in fact a circular button drawn out while 

 viscous into an elongated ellipse. This, as well as several 

 other specimens of the normal circular buttons, was obtained 

 by Mr. Simson from Thomas Plains. That from Long 

 Plain is also of an abnormal shape. It was found in the 

 alluvial quartz drift of Smith's Creek, ten feet from the 

 surface, when sluicing for gold in the year 1891. It is 

 sub-cyclindrical or bolt-like, somewhat constricted in the 



* " Obsidian . . . has been found in circular and concave or buttondike 

 flakes of an intensely black colour in stanniferous drift, apparently igneous 

 ■ ejectamenta, Thomas Plains." Cat. Minerals of Tasmania. W. F. Petterd, p. 64. 



