[ m ] 



white, grey, or brown, often with round fpots, of 

 a different colour from the ground; fometimes 

 contains cryftals of fchorl, or feltfpar, not com- 

 pletely melted; fraclure rather more granular 

 than that of glafs. 



c. §cori<z\ compounded of iron and ftony niak. 

 ter, and owe their fufion to fulphu rated iron ; 

 they are tumefied and expanded by the fuiphure- 

 ous vapours ; colour generally black ; fometimesf 

 reddtfh from the calcination of the iron ; furface 

 rough, and uneven j texture cavernous ; the 

 cavities larger and more irregular than thofe of 

 cellular lava, but never fibrous. 



d. Slaggs, refemble the drofs of forges, gene* 

 rally red and heavy. 



rut 



