MODE V. GRANITE. 1 79 



fact can there be any just science, if terms be 

 used in a lax acceptation; and it is far better 

 to err in the contrary extreme, which can only 

 be accomplished by increasing the number of 

 distinctions and denominations, as has been done 

 in gemmology. 



As siderite has been shown to be among the Granite, with 



sidente. 



most primeval substances, and is found enclosed 

 in the crystallisation of the most ancient gra- 

 nites, so as to evince a priority of formation to 

 the quartz, or the felspar, which never appear 

 to be intercepted by the siderite; so it may be 

 assumed that a granite, consisting of felspar, 

 quartz, and siderite, with or without the addition 

 of mica, may be regarded as among the most 

 ancient, if not absolutely primary. Saussure 

 observes that there is no mica in the granite on 

 the summit of Mont Blanc, its place being sup- 

 plied by siderite ; and remarking the same dif- 

 ference to occur in the granite ejected from the 

 depths of the Italian volcanoes, he is led to the 

 reasonable conclusion, that this construction, 

 being found at the greatest heights and the 

 greatest depths, must be the most primordial. 

 It is also remarkable, that as the nucleus of the 

 earth is inferred by astronomers and natural phi- 

 losophers to consist of iron, which is seldom 

 found free from silex, so a great part of the sura- 



N 2 



