{ 239 ) 



found it after they had been expofed for 

 feme time to the fire. This exclufive pro- 

 perty of the Euganean micas is therefore a 

 proof that they have felt the influence of 

 this agent, and is a ftrong confirmation of 

 their volcanization. 



Before I difmifs the quarries of Monte 

 Merlo, I fhall briefly ftate two facSts not 

 undeferving the attention of the readen 

 Firft, it is not unufual to find within the 

 granitous lava nodofities of pure quartz, of 

 the thicknefs of one, two, and fometimes 

 even five inches. Befides giving fparks 

 plentifully with fteel, which is the peculiar 

 property of this ftone, it has a colour lightly 

 amethyfline ; it is tranfparent, fomewhat 

 und:uous to the touch, folid, and of an in- 

 determinate figure. But to what are we to 

 attribute the exiftence of thefe quartzofe 

 nodofities, which are uninjured, within this 

 volcanic granite ? I cannot perfuade my- 

 felf that they exifted in it previous to its ig- 

 nition ; fmce, had this taken place after- 

 wards, it mufl; have altered the quartz, by 



• depriving 



