XIII. ] ORIGIN OF CRYSTALLINE ROCKS. 291 



Protests against the views of this school have, however, not 

 been wanting. Scheerer, in 1846, in his researches in Polymeric 

 Isomorphism,* attempted to show that iolite and aspasiolite, 

 a hydrous species which had been looked upon as resulting 

 from its alteration, were isomorphous species crystallizing to- 

 gether, and, in like manner, that the association of chrysolite 

 and serpentine in the same crystal, at Snarum in Norway, was 

 a case of envelopment of- two isomorphous species. In both 

 of these instances he maintained the existence of isomorphous 

 relations between silicates in which 3HO replace MgO. He 

 hence rejected the view of Gustaf Eose, that these serpentine 

 crystals were results of the alteration of chrysolite, and sup- 

 ported his own by reasons drawn from the conditions in which 

 the crystals occur. In 1853 I took up this question and en- 

 deavored to show that these cases of isomorphism described by 

 Scheerer entered into a more general law of isomorphism, 

 pointed out by me among homologous compounds differing in 

 their formulas by ?iM 2 2 (M = hydrogen or a metal). I in- 

 sisted, moreover, on its bearing upon the received views of the 

 alteration of minerals, and remarked : " The generally admitted 

 notions of pseudomorphism seem to have originated in a too 

 exclusive plutonism, and require such varied hypotheses to 

 explain the different cases, that we are led to seek for some 

 more simple explanation, and to find it, in many instances, in 

 the association and crystallizing together of homologous and 

 isomorphous species." f Subsequently, in 1860, I combated 

 the view of Bischof, adopted by Dana, that "regional meta- 

 morphism is pseudomorphism on a grand scale," in the follow- 

 ing terms : 



" The ingenious speculations of Bischof and others, on the pos- 

 sible alteration of mineral species by the action of various saline 

 and alkaline solutions, may pass for what they are worth, although 

 we are satisfied that by far the greater part of the so-called cases 

 of pseudomorphism in silicates are purely imaginary, and, when 

 real, are but local and accidental phenomena. Bischof s notion of 



* Pogg. Annal., LXVIII. 319. 



t American Journal of Science (2), XVI. 218. 



