1892.] which have been exposed to High Temperatures. 3i)D 



seen with a low power; these are more or less coated with opacite, 

 and set in a glass variable in character; in parts it is rather deep- 

 brown, in others fairly clear, almost colourless, but crowded either 

 with very minute and rather filmy microliths or with pale-coloured 

 belonites and granules of opacite (the last being sometimes in more 

 considerable quantities than one would have expected) ; now and then 

 it is simply a brown glass. In one fragment with multiple twinning 

 the lines indicating the composition faces can be traced in parts whicli 

 have ceased to act on polarised light. In some fragments, mainly 

 vitrified, spots occasionally may be observed which continue to be 

 doubly refracting, though rather feebly, appearing like faint white 

 clouds on a dark background. The ground-mass is studded with 

 minute fragments of quartz, perhaps with some felspar, set in a glass 

 full of cavities, the smaller being lined with opacite, as in the case of 

 the last- described rock.* 



Nearly forty years since, an attempt was made by Messrs. Chancy, 

 of Birmingham, to utilise basalt for various purposes, by meltings it* 

 and then running it into moulds, pouring it out in sheets, &c. R$f v-. 

 ence has often been made to these experiments, but, so far as I,ani< 4 

 aware, no detailed account was published, nor has any connected 

 study been made of the results. t It may be, therefore, of interest tp. 

 record the structure of some specimens which 1 have examined. Two 

 of these were given to me a short time since by J. T. Chance, Esq. 

 One of them is a large fragment, evidently part of a block which, has 

 been cast in a mould. It was labelled. " melted 1851 to 1854, devitri- 

 fied." J On the surface which was in contact with the mould is a film 

 of deep-brown glaze, like that of an over-burnt Staffordshire " blue~ 

 brick.'' The rock is dark, almost black, with a faint purple tinge, 

 generally compact, exhibiting slight traces of a crystalline structure 

 in one part. In it are a fair number of small cavities, more or less 

 spherical, and a few of rather large size, towards the exterior, very 

 irregular in shape. On microscopic examination the fpllowing con- 

 stituents are observed: (1) magnetite, very abundant in minute 

 grains, which, however, evidently are often cubes or octahedra ; ('4) 

 very numerous microlithic prisms, ranging up to about Q;002 inch m 



* Mica should be present, but I only find two flakes, and these are so much 

 altered as to be barely recognisable, having lost their characteristic dichroism, 

 and looking like bundles of yellowish fibres. 



f They are referred to for comparative purposes by Messrs. Jadd and Cole in 

 their important paper on the Basalt-glass (tachylyte) of the Western Isles of Scot- 

 land ('G-eol. Soc. Quart. Jl.,' vol. 39, p. 444); also by Mr. Waller, 'Midland 

 Naturalist,' vol. 8 (1885), p. 261. 



From 'lire's Dictionary of Arts,' &c., s.v. "Basalt," it would appear almost 

 certain that this specimen was " devitrified " by slow cooling, obtained by running 

 the molten material into moulds of sand contained in iron boxes, raised to a red 

 heat. 



