Correspondence. 181 



so long ago as 1836, described' the crystalline rocks of the neighbom^- 

 hood of Christiania ; and after detailing the various appearances pre- 

 sented by the granite, syenite, porphyry without quartz, amygdaloid and 

 basaltic rocks, eurite-porphyry, greenstones (diorites and aphanites), 

 and rhombic porphyry, came to the conclusion that all these rocks 

 were the result of metamorphic action. The metamorphic rocks of 

 Canada, which have been so ably investigated by Sir W. Logan and 

 his associates, abound in serpentines, diorites, hyperites, euphotides, 

 and granites, which, as Dr. Steriy Hunt observes, "have by most 

 geologists been regarded as rocks of igneous origin, whereas they 

 appear to be for the greater part undoubtedly altered sedimentary 

 layers or masses."^ Professor Eamsay has likewise adduced' striking 

 evidence of the metamorphic origin of the Cambrian quai^tz-porphyry 

 of Llanllyfni, and the granite of Anglesey. Similar references might 

 be multiplied, but I will only cite one more. Dr. Dana classes * under 

 the metamorphic rocks granite, syenite, hyperite, diallage-rock, 

 diorite, pyroxenite, etc., etc. His definition of metamorphic rocks 

 is — " they are made from the sedimentary rocks by some crystal- 

 lizing process." He adds "they are sometimes called plutonic, to 

 distinguish them from the true igneous rocks." It is strange that 

 Mr. D. Forbes, during his " careful examination of the literature 

 of the subject," should have overlooked the expressed opinions of 

 so noted a mineralogist and geologist as Professor Dana. 



Mr. Forbes objects strongly^ to my remark that " we must beware 

 of assuming an igneous character merely from the appearance of 

 veins ramifying from crystalline into granular non-igneous beds. 

 This may in general be an excellent test of eruptive origin, but it 

 certainly cannot always prove that the main mass, from which the 

 veins appear to have come, has been forcibly thrust into its present 

 position." If we are to take the sending-out of veins as an invari- 

 able test of igneous action, then we must believe that serpentine is 

 an intrusive rock, all other evidence to the contrary notwithstanding. 



1 See his memoir in the first number of the " Nyt Magazin for Naturvidenskaberne," 

 a translation of which (with notes by Professor Jameson) will be found in the 

 "Edinburgh Philosophical Magazine," Vol. xxiv., p. 387. 



^ Geology of Canada, p. 686. The Canadian geologists also describe certain 

 granites which they consider to be eruptive, designating them as intrusive granites, in 

 contradistinction to those having a metamorphic origin, which are termed indigenous 

 granites. 



^ Geology of North, Wales Mem. of Geol. Survey, vol. iii., pp. 140 et seq; 190 et 

 seq. After describing certain phenomena exhibited in the neighbourhood of the 

 quartz-porphyry, Professor Ramsay remarks that he can only account for these 

 appearances by the supposition that the beds associated with the quartz-porphyry have, 

 as it were, been partly eaten into by heat, and themselves convei'ted into porphyry. 

 He comes to similar conclusions in regard to the granite of Anglesey. 



* Manual of Geology, p. 74, et seq. 



* My critic represents me as i-efusiug any longer to accept the definition of eruptive 

 or intrusive rocks which geologists have been accustomed to give, viz., that they "are 

 such rocks as are met with apparently breaking through, protruding into, or sending 

 out ramifications, dykes, or veins, into the adjacent stratified deposits." Now all 

 that can be inferred from what 1 have said is, that some of these appearances are 

 simulated by metamorphic rocks, and in this I believe "most geologists will concur 

 with" me. 



