XIII.] ORIGIN OF CRYSTALLINE ROCKS. 323 



that, in his opinion, such rocks, once formed, may become the sub- 

 jects of epigenic pseudomorphism, and be metamorphosed, as sup- 

 posed by Bischof, Dana, and others, into serpentines, steatites, etc. 

 In this case his implied sympathy, in 1861, with the teachings of 

 Scheerer, who, in denying the epigenic origin of the serpentine asso- 

 ciated with chrysolite and many similar cases, had struck a blow, in 

 the language of Naumann, at " those cases of pseudomorphism upon 

 which the theory of metamorphism is grounded " ; and finally, his 

 congratulations to Delesse (who had just declared that often " the so- 

 called metamorphism finds its natural explanation in envelopment," 

 and asserted the view of Scheerer and myself that much of what 

 has been regarded as pseudomorphism has no other basis than the 

 observed associations of mineral species) could, in my opinion, ad- 

 mit of no other interpretation than the one which I in 1871 gave 

 to it. There is a confusion, not to say a contradiction, in these 

 expressed views of the venerable teacher, which it is not easy to 

 explain. 



Nothing has been further from my intention than to misrepresent 

 the views either of Naumann or of Dana ; and my error, if I have 

 fallen into one, arises from the difficulty of knowing their real 

 opinions upon the matters in discussion. Let Professor Dana de- 

 fine, as clearly as I have done, his present views as to the origin of 

 magnesian rocks, both those made up of chrysolite and pyroxenic 

 minerals, and those composed of serpentine, steatite and chlorite, 

 which he has supposed to come from an epigenesis of the former ; 

 let him tell us whether he holds the doctrine of pseudomorphic 

 metamorphism which he taught in 1845, 1854 and 1858, and. 

 which, as I have shown, was held by Delesse as late as 1857, or that 

 doctrine so long maintained by me, which the latter adopted in 

 1861. Such a definition would be eminently satisfactory to those 

 who look to him as a teacher in science, and would prevent any 

 further misconception or unintentional misrepresentation of his 

 views.] 



Professor Dana, having clearly defined the proposition that the 

 chemical alterations which are recognized in individual crystals are 

 to be conceived as extending to rock-masses, and having, more- 

 over, asserted that the principle of the identity of metamorphism 

 and pseudomorphism " bears on all crystalline rocks," is logically 

 committed to all the deductions as to the changes of rocks which 

 the transmutationist school has drawn from the supposed alteration 

 of minerals. By reference to the table of pseudomorphs in the 



