178 



incrustations. The aqueous vapors, discharged 

 through great spiracles, do not contain alkali in 

 solution, like the waters of the Geyser, in Ice- 

 land *. Perhaps the soda contained in the lavas 

 of the Peak acts an important part in the form- 

 ation in these depositions of silex. There may 

 exist in the crater small crevices, the vapors of 

 which are not of the same nature as those on 

 which travellers, employed at the same moment 

 in a great number of objects, have made expe- 

 riments. 



Seated on the northern brink of the crater, I 

 dug a hole of some inches depth ; the thermo- 

 meter placed in this hole rose rapidly to 42°. 

 Hence we may conclude what must be the heat, 

 that reigns in this solfatara at the depth of thirty 

 or forty fathoms. The sulphur reduced into va- 

 pour is condensed into fine crystals, which how- 

 ever are not equal in size to those Mr. Dolomieu 

 brought from Sicily -f\ They are semidiaphanous 

 octaedrons, with very brilliant surfaces, and of a 

 conchoidal fracture. These masses, which will 

 one day perhaps be objects of commerce, are 

 constantly bedewed with sulphurous acid. I 

 had the imprudence to wrap up a few, in order 

 to preserve them, but I soon discovered, that the 

 acid had consumed not only the paper which 



* Black, in Philds. Transact. 1794, p. 24. 

 f These crystals were four or five inches in length. Dre*e, 

 Cat. d'un Muse"e mineral, p. 21. 



