454 DOMAIN XII. VOLCANIC. 



these felspars are always inserted immediately 

 into these substances without any intervening 

 body. Here, however, the case is different j 

 every felspar is surrounded with a rind or coat- 

 ing, which, when it is extracted entire from the 

 enamel, appears to be a vitreous globule, about 

 one or two lines in diameter, of a clear cinereous 

 colour. If we break this globule, we find within 

 it the half-fused felspar, not divested of its coat- 

 ing, but forming one body with it. These glo- 

 bules are very numerous, and sometimes by their 

 confluence form groups; and they are very dis- 

 tinctly visible, on account of the black colour of 

 the enamel. 



Coating. " The manner in which this coating was 

 formed around the felspars, I conceive to be as 

 follows: when the enamel was fluid, and en- 

 closed the felspars, it acted as a flux to their 

 external parts, and combined with them; and 

 from this combination was the rind or coating 

 . produced, while the internal part of the felspars 

 had only undergone a semifusion, because it was 

 not in immediate contact with the enamel. 

 There can be little doubt but that the felspars 

 likewise existed in the perfect glass; but the 

 heat probably being more active in that than in 

 the enamel, they were completely dissolved, and 

 the entire mass reduced to one similar consist- 



