I 73 1 



In the Jt/iceous clafs we have quartz or cryftal in various 

 regular forms, which, if fufed at all, muft have been in the 

 thinneft fufion, to be enabled to afTume thofe - fliapes. Now 

 the ftrongefl heat that art can produce is fcarcely capable of 

 producing the flighteft emollefcence in pure quartz ; how then 

 can we afTume that nature, in the mofl unfavourable circum- 

 ftances, could produce a perfeift fufion of that fubflance ? 

 Volcanos afford the moft intenfe natural heat with which we are 

 acquainted ; yet the mofl flurdy volcanifts allow it to be infufible 

 in thefe. In faft it is frequently found in circumflances in 

 which it is impofTible, confiftently with the known laws of 

 nature, to attribute its origin to igneous liquefadlion ; for 

 inftance, it is frequently found cryftallized in company with 

 calcareous fpar, fluors, lead ores, &c. on ftones of a mixed 

 nature, as Petrofilex, Hornblends, &c. Now it is well known 

 that though pure quartz or fpars will not melt alone, yet in 

 company with flones of another kind they will readily melt 

 and unite into one common mafs ; when, therefore, they are 

 found in diflindl maffes, clofe by each other, it is evident that 

 they were not formed by fufion, but in fome other manner ; 

 and there is no other than aqueous folution. Of this they bear 

 the marks, for they decrepetate for the mofl part when heated, 

 and become opake from the lofs of their watery particles ; 

 though the quantity of thefe involved in their texture be 

 exceeding minute. Have not fliells and chalk, and even water, 

 been found inclofed in filex * ? The imprefTion of fliorls has 

 Vol. V. K often 



• 41 Roz. 34. Mem. Dijon 1783 per Camui. 



