402 DOMAIN XII. VOLCANIC. 



down to that of the finest powder ; and is a 

 porous lava, light, tender, and somewhat re- 

 sembling an argillaceous substance, which is 

 astringent to the tongue ; some of the grains are 

 hard lava, heavy, ferruginous, and in round 

 particles. Nearly half of this first volcanic rain 

 consisted of very fine powders; these, seen 

 through a microscope, appear to be composed, 

 1. of crystals of black schorl*, which partially 

 retain their prismatic shape, and are partially 

 eaten by rust; 2. vitreous grains of similar 

 schorl ; 3. grains of lava which have undergone 

 alteration, and are reddened or whitened by va- 

 pour; 4. crystals of felspar, detached, and al- 

 though somewhat decomposed, preserving their 

 rhomboidal form ; 5. other crystals of felspar 

 adhering to lava, changed and covered with 

 farina externally, but internally untouched ; 6, 

 fragments of lava with small crystals, similar to 

 the arsenical ruby; 7. others incrusted with 

 flowers of sulphur; 8. vitrifactions of no regular 

 figure, porous vitrifactions, and a species ol 

 black glass or obsidian, transparent at the edges 

 and of a dark green colour. 



" The matter here analysed was collected ofl 

 the snows of the crater at Trifoglietto. 



* Schorl was then a name for siderite, or hornblende, P. 



