€hap. I.] 
OEIGIN OF THE PEIMEVAL EOCKS. 
3 
shale into mica-schist, as seen in the Secondary and even in the Tertiary- 
rocks of the Alps*. 
Elementary works, indeed, will have informed the student that such 
mutations of the original sediment have been generally accounted for by 
the supposed influence of great heat proceeding from the interior of the 
earth, and which at different periods had manifested its power in the erup- 
tion of granite, syenite, porphyry, greenstone, basalt, and other substances 
formed by fusion. Let it, however, be understood, that the prodigious 
extent to which the metamorphism of the original strata has been carried 
in mountain- chains, and at various periods through all formations, though 
often probably connected with such igneous evolutions, must have resulted 
from a far mightier agency than that which was productive of the mere 
eruptions of molten matter or igneous rocks. Many of the latter are, in 
fact, but partial excrescences in the vast spread of the stratified crystal- 
line rocks, — accompanying symptoms of the grander changes which re- 
sulted from deep-seated causes, probably from heat, electricity, and pres- 
sure, lateral as well as vertical, acting upon humid deposits with a power- 
ful intensity. 
Processes now going on in nature on a small scale, or imitated artifi- 
cially by man, may enable us to comprehend imperfectly in what manner 
some of these infinitely grander ancient metamorphoses were effected ; and 
experimental chemistry, when more extensively applied to the analysis of 
rocks, will, it is hoped, some day reveal still more important truths in this 
very obscure subject among ancient geological phenomena. 
But speculations on such physical operations are not here called forf. 
The main design of this work is to mark the most ancient strata in which 
the proofs of sedimentary or aqueous action are still visible, — to note the 
geological position of those beds which in various countries offer the oldest 
ascertained signs of life, and to develope the succession of deposits that 
belong to such protozoic zones. In thus adhering to subjects capable 
of being investigated, it will be seen that Geology, modern as she is among 
the sciences, has revealed to us that, during periods immeasurably long 
anterior to the creation of the human race, and while the surface of the 
globe was passing from one condition to another, whole races of animals, 
the several groups being adapted to the physical conditions in which they 
lived, were successively created, lived their appointed time, and perished. It 
is to the first stages only, or Palaeozoic, of these grand accumulations, 
and to the creatures entombed in them, that attention is now to be 
directed. 
The convictions at which I have arrived being the result of many years 
of research, I have been induced to give a condensed, and, as far as prac- 
* See my memoir on the Alps, Apennines, and periods, will find them well explained in the pro- 
Carpathians, Quart. Journ. Geol. Soc. vol. v. p. 157 found essay of the late Mr. William Hopkins of 
e t se 1- Cambridge, " On the causes of changes of climate 
t The reader who desires to study the laws by at different geological periods," Quart. Journ. 
which the superficial temperature of the earth has Geol. Soc. Lond. vol. viii. p. 56. 
been regulated in the immensely long geological 
B 2 • 
