XIII. ] ORIGIN OF CRYSTALLINE ROCKS. 293 



lites, etc., as being, all of them, the results of metamorphic epi- 

 genesis, and not original rocks. It is precisely because pseudomor- 

 phism has been so often confounded with metamorphism, that this 

 error has found acceptance. I only admit a pseudomorph where 

 there is some crystal the form of which has been preserved. There 

 are very many metamorphic substances which are in no sense of 

 the word, pseudomorphs. Had the name of crystalloid been chosen, 

 instead of pseudomorph, this confusion would certainly have never 

 found its way into the science. I think, with you, that the envel- 

 opment of two minerals is most generally explained by a contem- 

 poraneous and original crystallization. Secondary envelopments, 

 however, exist, and such may be called pseudomorphs or crystal- 

 loids, if they reproduce exactly the form of the crystal enveloped, 

 whether this last still remains, or has entirely disappeared." * 



It is unnecessary to remark that the view of Delesse and 

 Naumann namely, that the so-called cases of pseudomorphism, 

 on which the theory of metamorphism by alteration has been 

 built, are, for the most part, examples of association and envel- 

 opment, and the result of a contemporaneous and original 

 crystallization is identical with the view suggested by 

 Scheerer, and generalized by myself long before, when, in 1853, 

 I sought to explain the phenomena in question by " the associa- 

 tion and crystallizing together of homologous and isomorphous 

 species." 



Later, in 1862, I wrote as follows : 



" Pseudomorphism, which is the change of one mineral species 

 into another by the introduction or the elimination of some element 

 or elements, presupposes metamorphism (i. e. metamorphic or crys- 

 talline rocks), since only definite mineral species can be the subjects 

 of this process. To confound metamorphism with pseudomorphism, 

 as Bischof and others after him have done, is therefore an error. It 

 may be further remarked, that, although certain pseudomorphic 

 changes may take place in some mineral species, in veins and near 

 the surface, the alteration of great masses of silicated rocks by such 

 a process is as yet an unproved hypothesis." t 



* Bull. Soc. Geol. de France (2), XVIII. 678. 



t Descriptive Catalogue, Crystalline Rocks of Canada, p. 80, London Ex- 

 hibition, 1862 ; also Canadian Naturalist, VII. 262 ; Dublin Quar. Journal, 

 July, 1863 ; and American Journal of Science (2), XXXVI. 218. 



