398 Murchison’s Siluria. 
—=still less any trace of life-—has been deciphered by human 
abor.* 
The design of this work is much more attainable. Its aim is 
to mark the most ancient strata in which the proofs of sediment- 
ary or aqueous action are still visble,—to note the geological po- 
sition of those beds which in various countries offer the first as- 
certained signs of life, and to develop the succession of deposits, 
where not obscured by metamorphism, that belong to such proto- 
zoic zones. In thus adhering only 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 cycles 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—each group adapted to the physical conditions in which 
they lived—were successively created and exterminated. It is 
to the first stages only of this grand and long series of former ac- 
cumulations, and to the creatures entombed in them, that atten- — 
tion is now directed. 
The convictions at which I have arrived being the result of 
many years of research, I have been urged by numerous friends 
to give a condensed, and, as far as is practicable, a popular view 
of the oldest sedimentary rocks and of their chief organic re- 
mains, and thus to throw into one moderate-sized volume the es- 
sence of my large works,t as sustained by the publications of 
many other authors. 
Geologists are now pretty generally agreed, that the oldest ot- 
ganic remains which are traceable, pertain to the lower division 
protozoic world has been attained. 
One of the chief steps which led to the present classification, 
as admitted by my contemporaries, was the establishment of the 
“Silurian System” of rocks and their imbedded fossils. Before 
to contain a few undescribed fossil fishes, Not only were the re- 
The reader who desires to study the laws by which the superficial temperature 
of the earth has been regulated in the fseeijenlaidy long subsequent geo: i de 
ods, will find them well explained in the profound essay of Mr. W. Hopkins, “On ” 
causes of changes of ¢limate at different geological periods,” Quart, Journ. Geo 
Soe. Lond., vol. viii, p. 56. ; 
+ See Silurian System, Murchison, 1839; and Russia in Europe and the Ural 
tains, by Marchiso ison, de Verneuil, and de Keyserling (J. Murray, 1845). 
