ol Fe 
- 
ORIGIN OF CRYSTALLINE ROCKS. 493 
is removed and replaced by a different material, are questions 
which the advocates of this fanciful hypothesis have not explained. 
As taught by Blum and Bischof, however, these views of the al- 
teration of mineral species have not only been generally accepted 
but have formed the basis of the generally received theory of rock- 
metamorphism. 
Protests against the views of this school have, however, not been 
wanting. Scheerer, in 1846, in his researches in Polymeric Iso- 
morphism,* attempted to show that iolite and aspasiolite, a hy- 
drous species which had been looked upon as resulting from its al- 
teration, were isomorphous species crystallizing together, and, in 
like manner, that the association of olivine 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 main- 
tained the existence of isomorphous relations between silicates in 
which 3HO replaced MgO. He hence rejected the view of Gustaf 
Rose that these serpentine crystals were results of the alteration 
of olivine, and supported his own by reasons drawn from the con- 
ditions in which the crystals occur. In 1853 I took up this ques- 
tion and endeavored to show that these cases of isomorphism 
described by Scheerer, entered into a more general law of isomor- 
phism pointed out by me among homologous compounds differing 
in their formulas by nM,O, (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 no- 
tions of pseudomorphism seem to have originated in a too exclu- 
sive plutonism, and require such varied hypotheses to explain the 
different cases, that we are led to seek for some more simple ex- 
planation and to find it, in many instances, in the association and 
erystallizing together of homologous and isomorphous species.” t 
Subsequently, in 1860, I combated the view of Bischof, adopted 
y Dana, that “ regional metamorphism is pseudomorphism on a 
grand scale,” in the following terms :— 
sible alteration of mineral species by the acti various saline 
and alkaline solutions, may pass for what aii 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 
“ The ingenious speculations of Bischof eren rps rin on the pos- 
of 
* Pogg. Annal., Ixviii, 319. 
+ Pogg. Annal., Ixviii, 319. 
