318 ORIGIN OF CRYSTALLINE ROCKS. [XIII. 



basin, soon led me to seek the origin of these rocks in the alteration 

 of previously formed uncrystalline magnesian silicates. This view 

 was set forth by me in the American Journal of Science for March, 

 1860 ((2), XXIX. 284). and more fully in the Canadian Naturalist 

 for June, 1860 (also in the American Journal (2), XXXII. 286), 

 where it was pointed out that steatite, chlorite and serpentine were 

 probably derived from sediments similar to the magnesian silicates 

 found among the tertiary beds in the vicinity of Paris, the so-called 

 magnesian clays. 



We have seen that these various novel views, put forth by me in 

 1859 and 1860, though totally different from those taught by De- 

 lesse in 1858, were integrally adopted by him in 1861. These dates 

 are circumstantially given in my address of last year, and yet Pro- 

 fessor Dana, in his review of it, charges me with " following nearly 

 Delesse" as to the origin of serpentine. He also asserts that I 

 " make Delesse the author of the theory of envelopment," when I 

 have there declared that the view of Delesse " 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 associa- 

 tion and envelopment, and the result of a contemporaneous and 

 original crystallization is identical with the view suggested by 

 Scheerer in 1846, and generalized by myself, when, in 1853, I 

 sought to explain the phenomena in question by the association and 

 crystallizing together of homologous and isomorphous species." To 

 Delesse, therefore, belongs the merit, not of having suggested the 

 notion of envelopment in this connection, but of having pointed out 

 the bearing of the envelopment of heteromorphous and amorphous 

 species on the question before us. 



Professor Dana moreover asserts that, while Scheerer is the only 

 one who maintains similar views to myself, I, in common with 

 all other chemists, reject the chemical speculations which lie at the 

 base of his views. On the contrary, unlike most chemists, who 

 have failed to see the great principle which underlies Scheerer's 

 doctrine of polymeric isomorphism, I have maintained (American 

 Journal of Science (2), XV. 230 ; XVI. 218) that it enters into a 

 general law, in accordance with which bodies whose formulas differ 

 by nM,O s or nH 2 2 may (like those differing by nir/ 1 2 ) have rela- 

 tions of homology, and moreover be isomorphous. (See, further, 

 Paper XVII. of the present volume.) The existence of these same 

 relations was further maintained and exemplified in a paper on 

 Atomic Volumes, read by me before the French Academy of 



