APPENDIX. 623 



a fact that the spots and the lineaments of a blackish tint are 

 harder in a certain degree than those which are red j this is 

 most evident after the stone has been submitted to a polish, 

 and is exposed to a favourable light. The black parts are 

 then seen to be slightly saliant, and to exhibit, notwithstand- 

 ing the whole stone receives a beautiful polish, a glossiness 

 more lively and more brilliant than the rest of it. 



The globules enclosed in this porphyry are of a flesh colour 

 varying in shade, with radii diverging from the centre to the 

 circumference, traced by lines of a more evident colour than 

 the rest of the globule, and rather blackish ; these lines irra- 

 diate from a kernel in the centre, of a uniform but more red 

 colour than the rest of the globule. A broad circular line, 

 almost white, or but fkintly tinged with red, surrounds each 

 globule, and determines the circumference. But, in order to 

 obtain all these results in the best manner, on sawing the 

 specimens care should be taken to divide each ball as nearly 

 as possible in the centre, so that the kernel may appear : the 

 balls thus cut take an exquisite polish, which exhibits in a 

 plain manner the effect of this singular system of globular 

 crystallisation. 



No. 3. A perfectly spherical ball, accidentally separated from 

 the rock; it is three inches and six lines in diameter; a 

 circle five lines broad, and uniform in its breadth, surrounds 

 {he exterior of the bail, which is composed of a kind of hard 

 felspar, analogous to that of the matrix, but of which the 

 points, of a reddish colour, are very small. All these present 

 imperfect crystallisation act divergent rays. 



A second circle, two lines and a half in breadth, of com- 

 pact felspar of a fawn-coloured white, is enclosed within 

 the external circle, and the rest of the ball is only an assem- 

 blage of crystals of compact felspar of a somewhat deeper 

 tint, which direct to a common centre : I had this separated 

 ball cut into two equal parts. \ 



No. 4. In a beautiful specimen composed of three large 



