36 KOCK-METAMORPHISM, 



CHAPTER VII. 



THE METHYLOTIC ORIGIN OF OPHITES. 



WITH respect to the rocks now entered upon, we have evi- 

 dences in the pseudomorphic origin of their essential mineral, 

 serpentine, that something more than ordinary metamorphism 

 has been' concerned in developing their present chemical cha- 

 racters. 



According to Bischof, " When pseudomorphs show that a 

 mineral, B, may originate from another mineral A, it is possible 

 that, under suitable conditions, all minerals corresponding to 

 A, may undergo such an alteration in the rock where they occur. 

 This may be the case even where the former mineral is not in 

 a crystalline state, but exists in the rock as an amorphous 

 mass"*. Hence, as serpentine is always the product of che- 

 mical change, it follows that a rock, when it is entirely or 

 essentially composed of this mineral, must have had a pseudo- 

 morphic or, more properly speaking, a methylotic origin. 



This doctrine, applied to ophite, has been decidedly opposed 

 by Sterry Hunt, who, having rejected the pseudomorphic origin 

 of serpentine, both as a mineral and a rock, maintains that, 

 in the latter case, it is a chemical precipitate, like the gneisses 

 and other metamorphics usually associated with it. On the 

 contrary, it is seldom that any other mineralogical geologist 

 speaks of serpentine or ophite otherwise than as being a pro- 

 duct of chemical alteration. 



Blum considered there was good reason for believing all ser- 

 rjentine rocks, including their contained minerals, to be of this 

 origin. Referring to the presence of pseudomorphs after augite 

 at Monzoxii, in the Tyrol, he states "it is not merely the 



* Chem. & Phys. Geology, Engl. eel. vol. iii, pp. 65, (50. 



