324 ON THE IGNEOUS METAMORPHOSIS [Ch. XIV. 



as gneiss, in the conglomerates of the oldest fossiliferous 

 groups.* 



But even conceding these points, it may be presumed that 

 the debris, of which this fragmentary rock consists, was pro- 

 duced from the crystalline slates by causes similar to those 

 now in action : turn, then, to decomposing primary slates (the 

 supposed metamorphic schists, which are now interposed 

 between the granite and unchanged greywacke), and it will 

 be found that the oxide of iron contained in the perfect rock 

 has become a peroxide, and the greater part of the alkali has 

 disappeared from the argillaceous mass ; and then explain how 

 a degree of heat short of fusion could have reduced the metal 

 to a lower degree of oxidation, and have restored the alkali 

 to the felspar, in which mineral these crystalline rocks 

 abound ? 



We are likewise called upon to admit that the Hartz 

 furnishes similar evidence in favour of the metamorphic in- 

 fluence of the granite. Thus, according to M. C. Zincken, 

 the strata of hornfeh, which surround the granitic masses of 

 the Ramberg and Rosstrap mountains, are, for the most part, 

 igneous modifications of greywacke ; the granite intersects 

 these strata at various angles, and penetrates them in the 

 form of veins, near which the laminae of the slate are some- 

 times broken and bent, and fragments of the hornfels are 

 imbedded in the granite : in short, the phenomena are such 

 as commonly occur in Cornwall, and other countries, at the 

 junction of the granite and slate, f According to this state- 

 ment, it is supposed that granite has been violently injected 

 among the strata, in a state of igneous fusion : but from the 

 observations of Bonnard on the Hartz, of Brochant on the 

 Alps, and of Von Buch on Norway, it might be concluded 

 that the granitic masses of these countries are not distinct 

 formations, being often regularly instratified with the ad- 

 jacent schistose rocks, into which they on all sides gradually 



* Principles of Geology, vol. iii. p. 359. 



f Bulletin de la Soc. G^ol. de France, tome iii. p. 32. 



