Ch, II.] 



ORIGIN OF THE PRIMARY ROCKS. 11 



their ruins, They rise up from beneath the rocks of mechanical 

 origin, entering into the structure of lofty mountains, so as to 

 constitute, at the same time, the lowest and the most elevated 

 portions of the crust of the globe. 



Origin of primary rocks. Nothing strictly analogous to 

 these ancient formations can now be seen in the progress of 

 formation on the habitable surface of the earth, nothing, 

 at least, within the range of human observation. The first 

 speculators, however, in Geology, found no difficulty in ex- 

 plaining their origin, by supposing a former condition of the 

 planet perfectly distinct from the present, when certain chemi- 

 cal processes were developed on a great scale, and whereby 

 crystalline precipitates were formed, some more suddenly, in 

 huge amorphous masses, such as granite ; others by successive 

 deposition and with a foliated and stratified structure, as in 

 the rocks termed gneiss and mica-schist. A great part of 

 these views have since been entirely abandoned, more especially 

 with regard to the origin of granite, but it is interesting to 

 trace the train of reasoning by which they were suggested. 

 First, the stratified primitive rocks exhibited, as we before 

 mentioned, well-defined marks of successive accumulation, 

 analogous to those so common in ordinary subaqueous deposits. 

 As the latter formations were found divisible into natural 

 groups, characterized by certain peculiarities of mineral com- 

 position, so also were the primitive. In the next place, there 

 were discovered, in many districts, certain members of the 

 so-called primitive series, either alternating with, or passing 

 by intermediate gradations into rocks of a decidedly mechani- 

 cal origin, containing traces of organic remains. From such 

 gradual passage the aqueous origin of the stratified crystalline 

 rocks was fairly inferred ; and as we find in the different strata 

 of subaqueous origin every gradation between a mechanical 

 and a purely crystalline texture ; between sand, for example, 

 and saccharoid gypsum, the latter having, probably, been pre- 

 cipitated originally in a crystalline form, from water containing 

 sulphate of lime in solution, so it was imagined that, in a 



