46 KOCK-METAMORPHISM. H't^r: 



origin, we shall merely make a few brief remarks on those 

 which were originally ordinary igneous rocks. 



As seemingly favourable to the general view formerly held 

 respecting the origin of the Connemara ophites, our attention, 

 as already stated, was called some years since to the occurrence 

 of the Canuaver serpentinyte under circumstances demonstrative 

 of its being an "irruptive rock" that had undergone meta- 

 morphism. We agree with Mr. Kinahan in this view ; for, 

 whether originally consisting of tremolite or common diorite, 

 the rock, which must be regarded as having been igneous in the 

 first instance, has become changed, through methylosis, into a 

 mass of serpentine*. 



In 1876, after an examination of the Lizard in Cornwall, we 

 showed in a precited memoir that the serpentinyte occurring 

 there was originally an igneous rock, related to the porphyritic 

 wackite or dolerite of Bufaure. 



Continental geologists have been largely influenced in their 

 belief as to the origin of ophites by the occurrence of rocks oi 

 the kind, in the form of dykes, in Northern and Central Italy 

 and other countries. At Prato, Imprunetta, Volterra, &c., in the 

 Bay of Spezzia and the adjacent districts, euphotides, dolerites, 

 and other eruptive masses are more or less serpentinized into 

 ophites ; so that the Chevalier Jervis, in stating that the latter 

 are direct igneous products, expresses the opinion prevalent 

 among Italian geologists f. 



Allport, whose microscopic researches among the basaltic 

 dykes of England, Scotland, and Ireland have done much to 

 establish the pseudomorphic origin of serpentine as a mineral, 

 has brought forward numerous evidences which equally show 

 that these masses are convertible into ophites. 



Dr. Heddle, one of the latest writers on the subject, has made it 

 clear, as previously noticed, that many of the ophites of Scotland 

 were originally true igneous rocks. 



But for the eozoonal school it would seem superfluous to add 

 that the fact of some ophites having been originally sedimentary, 

 and others igneous, may be held to demonstrate that in both 

 kinds of rocks their miner alogical identity can only be due to 

 one and the same causation, methylosis. 



* The terms eruptive and igneous are to be taken in a conventional sense, 

 as applying to rocks not of sedimentary origin. 



t Mineral Resources of Central Italy, chap. iii. 1868, 



