( 2% ) 



as real glafs. The arpe(£t is faiooth and 

 Ihining, like that of glafs ; but with fome 

 undtuofity, as is the property of fome lefs 

 perfed: volcanic glafles. But on examining, 

 with greater attention, the pieces recently 

 fractured, we do not find in them the cha- 

 radleriftics of volcanic glafs ; as they have 

 not the finenefs of confidence, the undulat- 

 ing fuperficial ftreaks, the fharp edges, nor 

 the acute points. We may even handle and 

 prefs the flakes and fragments of them with- 

 out fear, wdiich cannot be done with impu- 

 nity by volcanic glaffes. 



We know, likewife, that the primordial 

 rocks, when they are changed by the ad ion 

 of fubterranean fires into the nature of glafs, 

 are no longer recognizable ; as they have 

 loft their primitive ftrudlure, and are redu- 

 ced, together with the extraneous fubflances 

 they contain, as flioerls and feltfpars, to one 

 fmiilar and homogeneous mafs; whereas, 

 on the contrary, the vein in queftion fuffi- 

 ciently declares its origin, which is a petro- 

 filex of a dark green colour, a fra6^ure 



fomewhat 



