402 Specimens of Rock exposed to High Temperatures. [Jan. 28, 



with a paler border, something like a fleur-de-lys in shape. But on 

 the whole the glass is remarkably uniform and free from mierolithic 

 enclosures of appreciable size. 



A fifth specimen consists of a number of small black glassy frag- 

 ments labelled " Melted Rowley Basalt, cooled in water. Eagle 

 Foundry, Birmingham, February, 1858." This material is not suited 

 for slicing, so I have had some of it pounded and have examined the 

 powder. This shows the rock to be a glass which breaks into rather 

 flat sharp-edged chips with a clean somewhat conchoidal fracture ; in 

 colour a translucent umber-brown, not dark in the thicker parts of 

 the fragments, and a very faint olive-brown, almost colourless, in the 

 thinner. One or two of the larger chips give slight indications of 

 a fluidal structure, and contain, rarely, a minute cavity or a granule 

 or two of opacite. 



All the basalt on which Messrs. Chance experimented came, I 

 believe, from the well-known mass near .Rowley Regis,* which has 

 been often described. The natural rock is usually fairly coarsely 

 crystalline ; but I happen to possess specimens of an unusually glassy 

 variety, collected by myself nearly twenty years since, from a pit 

 which was then being opened on the northern side of the hill, near 

 some collieries, which, as I was told, were called the California pits, 

 the excavation being evidently almost at the base of the basalt. 

 These specimens, macroscopically, are compact dark magma-basalts, 

 with rather smooth sub-conchoidal fracture, onef slightly more com- 

 pact than the other. Under the microscope we see in both, but more 

 commonly in the less compact, sparse grains of serpentinised olivine 

 and crystals of plagioclase, each about O'OO.S inch long, together 

 with grains of iron oxide (magnetite, or perhaps in some cases 

 ilmenite) scattered in a colourless matrix which is thickly studded 

 with smaller granules of iron oxide, and tiny, rather irregularly 

 formed prisms of almost colourless augite, among which the presence 

 of lath-like microliths of felspar is suggested. On applying polarised 

 light (with a magnification of about 50 diameters) much of the clear 

 part seems not to produce any depolarising effect, though obviously 

 felspar microliths are frequently present in it; but with about 

 150 diameters very faint bands of gray light make their appearance 

 most clearly in the coarser-grained specimen : in the other, even 

 when a quartz plate is used, no difference of tint can be seen in some 

 parts, either as the stage is rotated, or by comparison of the edge of 

 the slice with the coloured field. The indefinite, almost ghost-like 



* See Allport, ' Geol. Soc. Quart. Jl.,' vol. 30, p. 548. Mr. Rutley described 

 specimens of melted basalt from the Giant's Causeway, and from Kilauea and 

 Mokua Weo-Weo, in the Hawaiian Islands. 



t The first obtained, for I visited the quarry a year or two afterwards, when it 

 had been considerably enlarged. 



