NOME XI. GRANITE AND GRANITIC PORPHYRY. 179 



which I have long combated the precision. Pri- 

 mitive mountains have often shown him, as well 

 as myself, many rocks which have united the two 

 modes of being, and which seemed to be inter- 

 mediate species between real granites and real 

 porphyries; and to point out the gradations by 

 which nature passes from the formation of the 

 one to the other. How many rocks have I not 

 observed, which, by their polished surfaces, 

 showed the texture attributed to porphyries, by 

 distinct and isolated crystals, forming spots on a 

 base apparently compact, and of a different co- 

 lour; while their fracture represented grains of 

 granite, by the scaly tissue of the substance 

 which had appeared to be the paste, in which 

 the other substances were enveloped; for granites 

 have a granular appearance, not always by the 

 detachment of the grains of each of the sub- 

 stances which compose them, but by the nature 

 of the texture of the felspar, of which the plates 

 cross each other when confusedly crystallised* : 

 and in all compound rocks, the substance which 



* " It is equally on account of their scaly tissue that sparry 

 marbles, called saline,, seem formed of large grains, adhering toge- 

 ther by juxtaposition. They owe the appearance of it to a confused 

 crystallisation, which interlaces the sparry plates ; and they lose this 

 granular aspect, to assume that of a compact and uniform mass, 

 when they are deprived of this commencement of regular aggre- 

 gation." 



