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fary *. Sauflure tells us, that a fpotted lava 

 (lave a ocil de perdr'ix) which he found on 

 Monte Somma, acquh-ed, after fufion, a black 

 vitrified ground, but that the polyhedrous 

 grains of this lava remained unchanged in 

 the moft violent fire ; and by polyhedrous 

 grains it is evident that he means what I and 

 others have called garnets f . With refpe^fi 

 to the adion of oxygenous gas upon them, 

 we may refer to Ehrmann, in his work on 

 the Air of Fire. " The white opake garnet of 

 " Vefuvius," fays this writer, " differs from 

 " garnets properly fo called, in this, that it 

 " melts with extreme difficulty (with the 

 " affiflance of oxygenous gas is here to be 

 " underftood), and at length, after continual 

 " ebullition, becomes a mafs perfedly fimi- 

 " lar to quartz, even in its fradure, and 

 " which crackles in like manner between 

 " the teeth." 



This kind of ebullition I have obferved 

 in the four varieties of garnets above men- 



* De ProducElis Vulcanlcis. 



t Voyage dans les Alpes, Tom. I. 



doned, 



