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 
