NOME VI. OBSIDIAN. 459 



of the latter by the Abbe Fortis; but I find that, 

 excepting their globose figure, they differ in 

 every respect from those of which I now speak. 

 The globes of Ponza are composed of leaves 

 over leaves of an imperfect enamel, do not give 

 sparks with steel, and contain felspars and mi- 

 ca ; whereas those of the Monte della Castagna 

 rarely include a few felspars, give sparks with 

 steel, have a vitreous appearance, and are not 

 composed of plates or leaves. 



" Some pieces of this enamel, broken and de- 

 tached from the masses, are in one part true 

 enamel, and in another lava. The latter gives a 

 few sparks with steel, has a grain approaching 

 to earthy, and, as far as I could discover, has for 

 its base a soft horn-stone, from which conse- 

 quently the enamel likewise derives its origin. 



" These are the principal vitrifications I ob- 

 served in my excursions to the Monte della Cas- 

 tagna. Some I have omitted to notice, since, 

 some trifling differences excepted, they are es- 

 sentially the same with those described. It is 

 proper, however, to remark, that more than one 

 of them exhibits manifest signs of having once 

 flowed down the sides of the mountain, in the Currents, 

 thick threads and vitreous filaments they con- 

 tain, similar to those we see, on a lesser scale, 

 in glass fused in our furnaces, when it comes 



