IVALY. LETTER XI. 145 



5. Lamellated black jberl-glimmer, in larger or 

 fmaller often hexagonal lamellae ; fplendent -, feem 

 to be fragments of columnar fherl. 



6. Black fieri fprinkled in the lava in fmali 

 points. 



7. Small, black, prifmatical, hexagonal merl- 

 cryftalsi fplendent; their form but appearing under 

 the microfcope ; wafhed by rain out of the volcanic 

 aflies ; either drawn by the load-ftone or mixed 

 with iron-fand. 



8. Green, either dark and blueim, or cryfolite, 

 or emerald-colouredyZ>r/, in hexagonal, pyramidi- 

 cat prifms j found in the black lava often of an inch 

 diameter-, of the hardnefsof fherl, or, at lead, of a 

 coloured quartz-cryftal, to whofe form it is refem- 

 bling , however, by the Neapolitans called gemma, 

 or precious fione. 



9. Yellow hyacinth, or topaz-coloured hexagonal 

 jloerl. This too is nearly as hard as a gem. 



All thefe merl-varieties, inclofed in the Vefuvian 

 and other lavas, feem to have been produced in 

 the lava during its fufion. My arguments are the 

 following. 



i. There is no example of any mountain or 

 rock, precipitated by water, and explored by 

 miners and mineralogifts, which is found to con- 

 tain fo amazing a quantity of (herl-cryftals, as are 

 inclofed in the lavas. The fmall numbers of the 

 L above- 



