APPENDIX. 



This variety of porphyry with small globules requires the 

 detail given of it, on account of its accompanying generally 

 the porphyry with large globules, which we are about to 

 mention ; or, more properly speaking, this is the rock itself, 

 in midst of which the latter is most commonly found in the 

 shape of thick walls which resemble veins, and which show 

 themselves in this manner only on account of their having 

 opposed a greater resistance to decomposition than the sur- 

 rounding rock with small globules. This rock, more abound- 

 ing in felspar, and of more homogenous texture, is, like all 

 felspar, subject to a species of spontaneous decomposition, 

 especially if iron, so prone to oxydation, be found in it, 

 either united or in combination, in too great a proportion. 

 The walls of globular porphyry have even more readily be- 

 come exposed, when they have chanced to be surrounded by 

 rocks of a greenish granulated porphyry, of a more tender 

 nature, and similar to those found at Oberstein; in the 

 Esterelle mountain ; and in general in most countries yielding 

 porphyry. 



No. 2. Spherical globules, two inches in diameter, the 

 smallest being of two inches wanting three lines, lying in 

 their gang, to which they closely adhere. 



This gang is compact, felspar, speckled with an ochry red of 

 different shades, with small spots of a blackish brown, and 

 can be considered, as well from its position as from its spe- 

 cial mode of formation, as no otl>er than a porphyro'id, and 

 not a jaspoid, for its parts are fusible under the blow-pipe. 

 Observing the small red spots through a microscope, one 

 sees distinctly that they are formed only by imperfect crystal- 

 lisations of a globular figure. The ground, of a blackish 

 brown, on which these diminutive globules, in an imperfect 

 state and of a reddish colour, appear, has this tint from the 

 iron, on its oxydation, assuming a blackish colour, whereas 

 in the globules the oxyd of the iron is red; but whether 

 there be a somewhat greater proportion of quart zy particles 

 in the small blackish spots than in those which are red, it if- 



