( =8? ) 



l^nfmaticaljand fometimes amorphous, whlcfi 

 give fparks ftrongly with fleel, and form very 

 brilliant plates. The hirged are live lines 

 and three quarters in length. Each of th^fe 

 feltfpars inchides within it a fmall portion of 

 the petroiiliceous bafe, which forms in it a 

 kind of nucleus, and occupies a confiderable 

 part of its fubftance. But to what caufe arc 

 we to afcribe this Angularity ? I can conceive 

 no other method of explaining it, but by 

 fappofrng, that when the integrant particles 

 of the feltfpars, diffeminated in the earthy 

 and liquid i^afe, united by the force of aggre- 

 gation in cryftallizcd mailes, each of thefe 

 jnafTes included a fmall part of tliis bafe, 

 greater or lefs in quantity. The rarity of the 

 phenomenon, however, fuppofes a local cir- 

 cum Ranee, which had a dire^^t relation to 

 this fmgular combination, and of the nature 

 of which I am ignorant. 



The feltfpars fufe in the furnace, and be- 

 come intimately mixed with the bafe in fuch 

 a manner, that the refult is a folid, white, 

 femi-traniparentglafs, with black fpots,occa- 



fioned 



