1*78 BOMAIN X. TRANSILIENT. 



which, in reality, only differ from granites b; 

 this accident of aggregation*. 



<c The distinction established between granite 

 and porphyries is proper for common use, it i 

 necessary for artists ; nevertheless the lithologis 

 could not admit it in a strict sense, without ex 

 posing himself to an error, which might lead bin 

 Granites, to mistake the identity of the origin of these twi 

 rocks, and the analogy of their composition 

 The celebrated naturalist (M. de Saussure), wb 

 has furnished us with a great and importan 

 truth, by proving, by a thousand excellent ob 

 servations, that the parts of granite are content 

 porary, that they have all been formed in the sam 

 element, and by the same cause, and that the prin 

 ciple of this formation is crystallisation $ but whi 

 has thought he ought to make two separate 

 genera of granites and porphyries, and who t< 

 distinguish them has said, in granite there is n 

 paste, which envelops the stony grains of which i 

 is composed, while in porphyries, is seen a uniform 

 base, or cement, in which the other stones are en 

 closed: this naturalist, I say, by the progres 

 of his researches, has soon himself found the in 

 sufficiency of these distinguishing characters, Q 



* This can only apply to granitic porphyries: and some othe 

 remarks must be pardoned, from the state of the science at tha, 

 period. 



