Remarks on Dr. Boase's Primary Geology. 547 



impose on their readers by false or flimsy statements founded on 

 mere terms." 



To return to Dr. Boase's description. He remarks : 



" In Cornwall the granitic rocks occur at the surface, in the form 

 of eight insulated masses, four of which are of much greater extent 

 than the others ; each of these masses presents some peculiarities, but 

 all of them contain several varieties of true granite. The most 

 general feature of the Cornish granite is the abundance of its fel- 

 spar, shorl however is the characteristic mineral of this district ; 

 indeed it is seldom altogether absent from these granitic rocks for 

 any extent, though it is often in such minute particles as to require 

 a magnifying glass for its detection. 



" Thus we learn that the granitic masses of Cornwall are not, as 

 some have supposed them to be, composed of one kind of rock, uni- 

 form in its constitution, and uninteresting in its varieties, but as 

 complex in their composition as the stratified rocks ; and in their 

 mineral transition into each other, afford us curious and instructive 

 subjects for investigation : on this account, the utility of mineralo- 

 gical distinctions is obvious ; and it will be still more apparent when 

 we consider these granitic rocks hereafter, not only in their relations 

 toward each other, but also towards the crystalline schists with which 

 they are associated." 



In his 3rd Chapter, Dr. Boase proceeds to compare the 

 granitic rocks of other countries with those of Cornwall, 

 wherever he is able to find minute mineralogicai descriptions 

 given in sufficient details for his purpose, and remarks : 



" Notwithstanding the paucity of such description, yet sufficient 

 data may be gleaned for our purpose, which is to show, that the 

 granitic rocks of other countries exhibit similar variations in their 

 mineral composition, and similar associations as those of Cornwall." 



And at the close of the chapter, 



" In concluding these brief details concerning the granitic rocks, 

 we will only observe, in addition to the remarks which have been 



4 B 



