HISTORY OF CRYSTALLINE ROCKS. 35 
deposits. The solvent action exerted by solutions of alkaline silicates on oxyds of iron, 
manganese, zinc, Magnesium, and calcium, as well as upon those of tin, antimony, copper, 
and mercury, throws, as elsewhere pointed out, an important light on this problem. ! 
To this we must add the dissociation of silicate of alumina at elevated temperatures, 
under pressure, in presence of alkaline solutions, with separation of silica in the form 
of quartz, as observed by Daubrée and Henri Sainte-Claire Deville’. These experimenters 
obtained at the same time Zeolites. and one of them pyroxene, apparently with magnetite ; 
while Friedel and Sarresin, under similar conditions, got orthoclase and albite, quartz 
and analcite. We are as yet ignorant under what circumstances the liberated alumina 
might be separated from these solutions as corundum or diaspore. The conditions of 
temperature, and the presence of alkaline solutions in these experiments, approach very 
closely to those which we have supposed to concur in the formation of mineral species by 
the crenitic process. 
§ 64. The geognostic and genetic history oi the great endogenous crystalline masses 
which we have now discussed in some detail is important for several reasons: 1. It 
brings before us the views of the plutonists, who see in great bodies of crystalline lime- 
stone, and of magnetite, as well as in granitic veins and in metalliferous quartz lodes, the 
evidences of ignecus eruption. 2. It shows the differences, alike mineralogic and geog- 
nostic, between true exotic rocks (which, with small differences in composition, have been 
erupted through widely separated geologic ages up to the present) and those endogenous 
deposits which are found only in eozoic rocks, and were formed in eozoic time, since their 
fragments are met with in the oldest overlying paleeozoic sediments. 3. It makes evident 
the close mineralogic resemblances between these endogenous crystalline masses and the 
more ancient enclosing rocks, and thus helps us to a clearer conception of the conditions 
under which these ancient gneissic strata, and the pre-gneissic granite itself, were alike 
generated. 
§ 65. The crenitic hypothesis, as we have seen, supposes that the granite, and the 
succeeding crystalline schists, have been built up by matters dissolved from a primary 
plutonic substratum, upon which, as upon a floor, through successive ages, was laid down 
the enormous thickness of crenitic rocks, which, with small exceptions, make up the pre- 
Cambrian terranes. The bearing of this hypothesis upon the great problem presented 
by the corrugated condition of the older crystalline schists has already been noticed in a 
previous essay.” The contraction of a cooling globe, which is often cited in explanation 
of this phenomenon, is clearly inadequate to account for this great and general corruga- 
tion of the strata, and the present writer in 1860 ‘ suggested, as a farther element in the 
explanation thereof, the condensation during crystallization of the mechanical sediments 
from which, in accordance with the Huttonian hypothesis, the crystalline schists were 
supposed to be derived. This explanation, based on an untenable hypothesis, must, how- 
ever, be rejected. The endoplutonist must appeal to contraction in the igneous mass of 
the globe as the only explanation of the corrugations of its outer envelope, while the 
exoplutonist adds thereto the diminution of the liquid interior as the result of successive 
transfers of portions of its mass by ejection of igneous material from beneath a first-formed 

! Trans. Roy. Soc Can., Vol. ii. Sec. iii. pp. 45 and 61. 
* Jbid., Vol. ii. See. iii, p. 49. * [bid., Vol. ii. Sec. iii. p. 60. 
* Amer. Jour, Science, xxx. 138, and Chem. and Geol. Essays, pp. 46, 71. 
