i m 3 



e. PiperinQ i a concretion of volcanic afhes, 

 $nd is faid to be the fubftance that covers Pom-f 

 peia; colour grey or reddifh brown; fra&ure eaih 

 thy ; contains fragments of white marble, feltfpar, 

 mica, garnets, fcoriae, gypfum, fchorl, granite, &c. 

 fometimes magnetic ; if preferved from moifture, 

 it hardens in the air. 



II. LAVA. 



Any matter that has iffued out of a volcano in 

 a liquified ft ate, or that has accompanied or been 

 enveloped in fuch Ijquified matter. Kirwan. 



a. Cellular ; colour brown, or greyifh black; 

 furface unequal, rough, and full of cavities ; af- 

 fects the magnetic needle. 



b- Compact ; earthy fubftance, or matter, which, 

 ^ifter having been fufed, but not vitrified, becomes, 

 pn cooling, compact, clofe, and folid. 



III. VITREOUS LAVAS. 



a. Glass ; fuch matter as has been expofed to 

 the greateft heat, and from the compofition, moft 

 fufceptible of vitrification in a moderate heat ; 

 colour black, green, yellow, or greyifh white ; 

 found in detached mafles ; either fpongy or com- 

 pact: fracture. 



b. Enamel ; refembling vitreous lavas, is 

 the imperfect vitrification called enamel ; colour 



white, 



