J 6 Lamination of Volcanic Rocks paet i. 



tain, at the base of which, they are situated ; and they 

 do not appear as if they had been inclined by violence. 

 A hisfh inclination is common to these beds in Mexico, 

 Pern, and in some of the Italian islands : l on the other 

 hand, in Hungary, the layers are horizontal ; the 

 lamina?, also, of some of the lava-streams above referred 

 to. as far as I can understand the descriptions given 

 of them, appear to be highly inclined or vertical. I 

 doubt whether in any of these cases, the laminse have 

 been tilted into their present position; and in some 

 instances, as in that of the trachyte described by Mr. 

 Scrope, it is almost certain that they have been origin- 

 ally formed with a high inclination. In many of these 

 cases, there is evidence that the mass of liquefied rock 

 has moved in the direction of the lamina?. At Ascen- 

 sion, many of the air-cells have a drawn-out appearance, 

 and are crossed by coarse semi-glassy fibres, in the 

 direction of the lamina?; and some of the layers, sepa- 

 rating the sphaerulitic globules, have a scored appear- 

 ance, as if produced by the grating of the globules. I 

 have seen a specimen of zoned obsidian from Mexico, 

 in Mr. Stokes* collection, with the surfaces of the best- 

 defined layers streaked or furrowed with parallel lines ; 

 and these lines or streaks precisely resembled those, 

 produced on the surface of a mass of artificial glass by 

 its having been poured out of a vessel. Humboldt, 

 also, has described little cavities, which he compares to 

 the tails of comets, behind sphaerulites in laminated obsi- 

 dian rocks from Mexico* and Mr. Scrope has described 

 other cavities behind fragments embedded in his lami- 

 nated trachyte, and which he supposes to have been 



1 See Phillips's ' Mineralogy,' for the Italian Islands, p. 136. 

 For Mexico and Peru, see Humboldt's ' Essai Geognostique.' Mr. 

 Edwards, also, describes the high inclination of the obsidian rocks 

 of the Cerro del Xavaja in Mexico, in the ' Proc. of the Geolog. Soc.' 

 for June, 1838. 



