152 TRAVELS THROUGH 



hard fherls are part of the precious ftones ; accord- 

 ingly, to avoid cheats and impoftures, this name 



is 



The Jberls are, according to the author's own evidence, 

 cryftallized in a fluid ftate of their matrix, produced either 

 by water or by fire ; their form cryftallized regular ; their 

 fubftance eafily melting before the blowing pipe ; and what- 

 ever be their origin, their hardnefs and gravity inferior to 

 that of the volcanic vitrification-pebbles, and of the precious 

 ftones. To thefe the Tranilator adds, that fome fherls are 

 endowed with the double electricity of the tourmaline, h^- 

 therto never obferved in the precious {tones; and that their 

 natural forms too are very different from thofe of the precious 

 Hones. 



The 'volcanic vitrification pebbles are immediate productions 

 of the fire, and conftantly found in the hardeft lavas ; en- 

 tirely deflitute of any regular cryfialline form of either the 

 fherls or precious ftones, being properly vitrifications of 

 fherls, as hinted by Mr. Rafpe's defcription of the Heflian 

 Volcanos ; their hardnefs and gravity above the fherls, and 

 nearly the fame as that of the coloured precious flones. 



The precious jlanes are aqueous cryftallizations of many 

 different regular forms ; unknown whether ever found in a 

 volcanic matrix j their fubflance remarkably refractory to 

 the fire j their hardnefs, gravity, and luftre, above the fherls ; 

 and if not fuperior to that of the volcanic vitrifications, they 

 are undoubtedly differing from them on account of their co- 

 lours, having them either higher and finer dyed, or entirely 

 different. 



To thefe obvious and natural mineralogical differences a 

 Jeweller might perhaps add a great many more. However, 

 it is very true, that the high prices of the precious jlones are 

 father owing to old fuperfiicion, their fcarcity, fancy, and 



euflom j 



