APPENDIX. 



IBocca Galeria the felspar, harder and of a deeper colour than 

 any where else, contains globules of a paler hue ; there also 

 are found most beautiful geods of a substance much more 

 indurated, which seem as if agatised, and are of a reddish 

 brow r n colour $ at Fornaci the same kind of geods, but of a 

 violet tint : these last are very bulky, some of them being 

 more than a foot and a half in diameter. 



" At Elbo, on the sea-shore, globules are found detached 

 from their matrices, forming a sort of insulated balls. It 

 appears that the action of the waves has been sufficiently 

 forcible to beat down, break, and wear away, blocks of the 

 porphyry ; but that the globules being much more hard, have 

 more strongly resisted degradation, and been cast on shore. 



" To conclude : this vast extent is entirely composed of 

 porphyrous rocks, intersected by numerous veins in the form 

 of walls, in which the globular system is every where mani- 

 fested j and this wide field for observation well deserves the 

 attention of skilful mineralogists, who could not fail of 

 making numerous discoveries." 



It now remains I should give a detail of the different 

 specimens of orbicular porphyry, presented to me by M. 

 Mathieu. 



No. 1. Porphyry of an isabella colour, with a very light 

 shade of the rose, the globules spherical, very small and ra- 

 diant, some of them encircled by a distinct line, others with- 

 out this distinct line, and united with the ground in such 

 manner as to seem to form but one body with their matrix. 

 The ground, which is felspar, very compact, and formed of 

 extremely small particles, receives an excellent polish, for it 

 is hard, but susceptible at the same time of decomposition, as 

 well from the oxydation of the iron it contains, as from other 

 causes. The largest globules of this porphyry are but four 

 lines in diameter, the smallest in general three. When this 

 stone is broken for the purpose of obtaining specimens, the 

 globules sometimes separate in a perfect state, and leave the 

 mark of their position in the stone. 



