ITALY. LETTER XVI. 22^ 



ground colour is dyed in different degrees. There 

 are fome almofl entirely Black. The fpots are 

 commonly fmall and oblong -, ibmetimes larger, and 

 then either oblong, that is, parallelepiped, or an- 

 gulated irregular. They are opaque, milky, and 

 compact feld-fpath, but of a fherl-nature, as ap- 

 pears by their parallelepiped form, and other ex-* 

 ternal marks-, hence, they feem to me to be a 

 middle fpecies of feld-fpath and fherl. The real 

 difference between fherl, feld-fpath, quartz, and 

 other flint, and garnet-fpecies, is but very fmall, 

 merely depending on fome admixtures (Cronfted. 

 Mineralogy). Sometimes there offer in the red 

 Porphyry blunted pieces of another porphyry-fpe- 

 cjes, with whiter ground and larger fpots. Thefe 

 adventitious pieces fuppofe the inclofing mafs to 

 have been ductile, as that of the Breccia. This 

 may be obferved on fome Porphyry columns on 

 the out-fide of S. Marco at Venice. There appear 

 likewife in it fome thin black fherl-feathers, as on 

 the pedeftal of the Diana triformis, in the capitol 

 at Rome. 



4. Porfido nero t black-white fpotted. There 

 are two varieties. 



a. Entirely black, with fmall oblong white 

 Porphyry-fpots ; the colour excepted entirely refem- 

 bling'the red Porpyhry. Of that kind there are 



two 



