546 Remarks on Dr. Boase's Primary Geology. 



granite, both essential and accidental, are united together by a con- 

 fused crystallisation, not only mutually penetrating and interfering 

 with each other, but sometimes the small crystals of one are com- 

 pletely enveloped in the large crystals of a different kind of mineral. 

 And it is a very common occurrence for one or even more, of these 

 minerals to be developed in large crystals in a granular basis of the 

 whole, so as to constitute a porphyritic granite. This character is 

 generally imparted by the felspar, and rarely by the quartz or mica." 



In his advocacy of such a hypothetical term as " True 

 Granite," it may be doubted if Dr. Boase may not himself 

 have fallen into the error which he blames in others. For the 

 term is totally uninteresting, and even unintelligible, unless 

 with reference to theoretical assumptions. On this point Dr. 

 Macculloch's remarks (System of Geology, Vol. II. page 81) 

 are peculiarly apposite : 



" The term granite has by some been limited to a compound of 

 quartz, felspar, and mica, and the word syenite, adopted for those 

 containing hornblende, laying the foundation of a large progeny of 

 errors. The distinction is as unfounded as it is pernicious. To the 

 first compound there is sometimes superadded hornblende, or else it 

 becomes a substitute for the mica, producing a granite even more 

 abundant than the first ; while the ternary compounds also loose one or 

 other of their ingredients, and become binary : all these varieties 

 further occurring on the same mass, and often within a very small 

 space. In nature, therefore, granite ranges within four essential 

 minerals, quartz, felspar, mica and hornblende, in different com- 

 binations of two, three or four. If this were merely a question of 

 mineralogy, the distinction, thus condemned, might be conceded 

 without inconvenience ; but as the nomenclature of rocks is a nomen- 

 clature for the purposes of geology, it is easy to see what fallacies 

 may intrude from an improper use of terms : as has happened from 

 that of syenite, thus making a distinct geological rock of any 

 granite which happens to contain hornblende. Thus have the latest 

 been confounded with the older unstratified rocks ; not only pro- 

 ducing inextricable confusion, but permitting trifling observers to 



