ITALY. LETTER XI. 141 



and calcareous fpar to a fubterraneous vein, and 

 therein to have been produced by water ; though 

 fome other fherl-cryftallifations in the holes of 

 lava, which I fhall notice after, and which owe 

 their origin to fire, are entirely fimilar to thefe. I 

 have obferved the following varieties. 



a. Polygone, pyramidical, fmdl Jherl-cryftallifa- 

 tions; form fimilar to blende; hardnefs and tex- 

 ture different i colour white, black, blackilh-green, 

 grafs or emerald green, purple or garnet-red, ruby- 

 red, brown, and topaz-yellow. Thefe, efpecially 

 the brown-coloured, are moil common in the 

 micaceous limeftone fpar, and are handed about, 

 and dearly fold as geros, though of a lefier hard- 

 nefs and pellucidity, and in fire affayed to be no- 

 thing but merl. The fame is to be faid of the 

 following three varieties. 



b. Sherl-cryftallifatiom in flat hexagonal trun-^ 

 cated pi'iirns -, black, dark-green, brown, and vi- 

 trefcent white. 



c. Sherl-cryftallifations in hexagonal prifms, 

 with a pyramidical top ; flat as the former ; en- 

 tirely fimilar to fmall quartz-cryftals j coloured 



as the before-defcribed (b). 



d. Globular polygone, or entirely garnet-like 

 Jherl-cryftals ; entirely fimilar to the white in 



the lavas. I doubt whether they juftly can be 



ranked amongft the raw pre-exiftent aqueous pro- 



2 duclions ; 



