246 Notice of Active and Extinct Volcanos. 



often present, and all these minerals are either confusedly united 

 without any apparent cement, or by the intervention of a paste 

 of a felspathic nature, sometimes compact, and sometimes cellu- 

 lar. This paste is generally light colored, though different 

 shades of red and brown are sometimes communicated to it by 

 the presence of iron, and there is one variety in which the paste 

 is perfectly black and semivitreous. intermediate in its characters 

 between pitchstone and basalt, but distinguished from either rock 

 by melting into a white enamel. Angite is sometimes present, 

 and grains of titaniferous iron are often discoverable, but olivine 

 rarely, if ever, occurs, and therefore appears to be the only min- 

 eral which has any claim to be considered as peculiar to basalt. 



" The second species, called by Beudant Trachytic Porphyry, 

 is distinguished from the preceding by the general absence of 

 scorified substances. Neither hornblende, augite, nor titaniferous 

 iron enter into its composition, but quartz and chalcedony, which 

 are wanting in the former, are commonly present in this species. 

 In its general aspect it bears a much nearer resemblance to the 

 older formations than trachyte properly so called. 



" This description however applies only to the characters of 

 the larger portion of the mass, for Mons. Beudant is compelled, 

 in order to include all the varieties, to establish two subspecies, 

 the one with, the other without quartz, and in both of these he 

 notices a variety possessing a vesicular structure. The subspe- 

 cies indeed, which is without quartz, even passes into pumice. 

 Many varieties of Trachytic Porphyry contain a number of very 

 small globules, which seem to consist of melted felspar, having 

 often in their centre, a little crystal either of quartz or of mica. 

 The assemblage of these globules, leaving minute ceils between 

 them, sometimes gives to the rock a scoriform aspect. The chal- 

 cedony often occurs in small geodes, and sometimes intimately 

 mixed with the paste in which the crystals are imbedded. 



" Trachytic porphyry also appears to pass by imperceptible 

 gradations into the next species, pearlstone which is characteri- 

 zed by the vitreous aspect generally belonging to its component 

 parts. It is evident, that this definition includes pitchstone and 

 obsidian, but these are of rare occurrence in Hungary, the great 

 mass of this formation being composed of the mineral called 

 pearlstone, some varieties of which pass into pumice. 



" In its simplest form, this rock presents an assemblage of 

 globules, varying from the size of a nut to that of a grain of sand, 

 which have usually a pearly lustre, and scaly aspect, and are set, 

 as it were, one upon the other, without any substance intervening. 



" From this, the most characteristic variety, the rock passes 

 through a number of gradations, in which its peculiarities are 

 more or less distinctly marked. In some varieties the globules 



