180 DOMAIN X. TRANSILIENT. 



is sufficiently abundant not to be divided by the 

 rencounter of other small stones mixed with it, 

 and for its parts to form a kind of continuity of 

 mass, in surrounding the other substances, of 

 which the grains are easily, isolated, may be con- 

 sidered as the principal base of the rock, or as 

 the cement which agglutinates the small stony 

 bodies, of a different nature, concurring to the 

 formation of the mass. Such are granites, where 

 felspar alone often constitutes three-fourths, 

 sometimes four-fifths of the mass ; and if an abs- 

 traction of the sparry tissue is allowed, which 

 depends on a rather more perfect aggregation, 

 and of which it may be deprived without chang- 

 ing its nature, the granular appearance of the 

 granite disappears, the felspar assumes the aspect 

 of a cement in which the other stones are enclosed^ 

 and the rock acquires the conformation of por- 

 phyry, without the transition of the one to the 

 other requiring any other condition. Nature 

 often, as if she would demonstrate the identity of 

 the two rocks, performs herself, in certain masses, 

 this successive transformation of granite to por- 

 phyry, by taking away and returning at inter- 

 vals its laminar tissue to the felspar ; and she 

 produces masses which, according to the ex- 

 pression of definitions, may be in part placed 

 among granites> in part among the genus of por- 



