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PROCEEDINGS OP PROVINCIAL SOCIETIES. 309 



ble that the crystallization takes place at a much lower temperature 

 (21°) than that necessary to fuse the glass, which is considerably 

 above 30" ; and this is the case not only with the glass of basalt, 

 but also in common green-bottle glass, which, when held in the fire 

 for some time, in a heat just sufficient to soften it, loses its vitreous 

 form, and becomes a substance of a mixed glassy and crystallized 

 structure, known as Reaumur's Porcelain. 



In the specimens of the melted mass exhibited by Dr. Ward, these 

 changes were very distinctly traceable. The first appearance observ- 

 ed in the glass was that of exceedingly minute, distinct, or clustered 

 globules, or spherules, of a grey colour, which, when examined by 

 a lens, exhibited a radiating structure, and a radiant brilliancy, 

 similar to that of wavellite or zeolite. As they increased in number 

 they pressed upon each other, till they became so numerous and 

 closely set as to resemble fish- roe ; and a still greater degree of 

 compression gave the whole mass the appearance of jasper or plum- 

 bago, though the separate globules might still be traced in it. Such 

 was the result where the development of the spherules was equal 

 and synchronous ; but in many parts of the glass they were observed 

 to be distinct, and these seemed to grow, by the addition of concen- 

 tric coats, to the number of three or more, like the coats of an 

 onion, but preserving their radiated structure. In the jasperine 

 substance, also, some spherules appeared to outstrip the rest in their 

 growth, and to absorb them, as it were, into themselves,, by shoot- 

 ing out their radii all round, and comprising them within the cir- 

 cuit of their new layers. But as the radii extended outwards, the 

 centre became more stony and amosphous in its appearance and 

 texture ; its colour deepened, and some appearance of crystals was 

 recognizable. The spherules, when of a certain size, but smaller 

 in the jasperine matter than in the glass, changed, also, in the polour 

 of their radii, which now assumed a brownish rusty tinge, somewhat 

 resembling brown haematite, from their being apparently covered 

 by a thin coating of rust, w^hich was also observable where two or 

 more were in contact, at the line of junction. Many of the spherules, 

 by their mutual compression, were formed into irregular polygons ; 

 and it was from observing this structure that Mr. Gregory Watt 

 framed his theory of the formation of basaltic columns. But at 

 this period the stony basaltic structure is not completed, for the radii 

 and concentric circles are still distinguishable, whereas in the co- 

 lumns nothing of the kind is discernable. The last change remarked 

 was the coalescing of the polygons into one mass, leaving the only 

 trace of their separate formations in their centres, now radiated in 

 crystals, and no longer in lines. This last form was not attained 

 nor believed to exist by Mr. Watt, as his experiment — being made 

 upon a less quantity of basalt, which was cooled more rapidly than 

 l^r. Ward's specimens — stopped short at the formation of the poly- 

 gons. Dr. Ward concluded his paper with a comparison of the 

 crystals and spherules of basalt with those observed in slags of glass, 

 iron, and other metals ; and hinted the possibility of imitating, by 



