130 POSITION AND NATURE OF [Ch. VII, 



their centres, parallel with the general strike of strata, N. E. 

 and S. W., it will be perceived that there are several lines or 

 axes many miles remote from each other. Whether this con- 

 dition of the Ocrynian ridge accords with all mountain-chains, 

 the granite of which is subject to like arrangements, we are 

 not prepared to answer : but this we know, that the Cornish 

 range is not a solitary example : " La recherche d'un axe 

 granitique," says M. Reboul, " me parait, jusqu'a ce jour, 

 avoir ete infructueuse. Les masses de cette roche forment au 

 sein des Pyrenees comme de grandes iles qui ne s'eloignent, 

 ni entre elles, ni avec 1'axe geographique," " Ainsi, la chaine 

 des Pyrenees, quoiqu'elle soit Tune des plus simples, est 

 neanmoins composee de plusieurs aretes qui affectent des 

 directions differentes, soit dans Talignement de leurs masses, 

 soit dans celui de leurs strates : et cette disposition Passim ile 

 aux autres chaines plus compliquees." * 



Having considered the relative position of the granitic and 

 schistose rocks, it is now proposed to examine the composition 

 and nature of these rocks at their junction ; and, as might be 

 expected, Cornwall also affords excellent opportunities for 

 this investigation. 



It has been already stated, in the description of the schistose 

 rocks, that those which immediately succeed the granite, 

 differ in their composition from those that are more remote ; 

 and so it likewise happens, that the beds of slate adjacent to 

 the granite generally assume a different aspect as they 

 come into actual contact with this rock. Thus, the slate of 

 the eastern district (proteolite) becomes more granular and 

 micaceous as it approaches the granite ; and the slate of the 

 western district (cornubianite) loses the fine-grained and 

 compact texture, so characteristic of this felspathic rock, 

 acquires a granular texture, and at the same time the acces- 

 sory mineral, whether mica, shorl, or hornblende, is developed 

 into distinct scales or crystalline granules, imparting to the 



* Bulletin de la Soc. Gdol. de France, tome ii. p. 79. 



