PEEFACE. 
vii 
It is unnecessary now to repeat the expression of my obligation to various 
persons who assisted me, either in the preparation of the ' Silurian System ' 
or the previous editions of this work ; for allusions are made to them in the 
body of the text, and these things are now part of scientific history. 
I have, however, a grateful and essential duty to perform, in stating that 
on this occasion I owe most to my accomplished friend Professor Eupert 
Jones, who has indeed been of vast service to me, as a well-read geologist 
and palaeontologist, and without whose skilful editorial aid in the prepa- 
ration of this volume many essential additions would have escaped me. 
To Mr. Robert Etheridge, the Palaeontologist of the Geological Survey, I 
am also largely indebted, not only for the support which he has given to 
the Devonian classification of Sedgwick and myself, by his Memoir on 
North Devon*, but specially for having enriched the Table of Fossils in 
the Appendix, originally prepared by Mr. Salter, by the enumeration of 
nearly three' hundred additional British species, many of them having 
been determined by the last named author. Mr. Etheridge has also, 
throughout the work, assigned their present names to numerous fossils. 
The reader will observe that, in the Tabular List of Silurian Fossils, I 
have used the term 4 Primordial Silurian,' instead of ' Lingula-flags,' the 
latter having only a local English meaning ; and as Lingulae occur in all 
formations, from the oldest Silurian to the present day, I have ceased to 
use the name : moreover some of these old Lingulidae are now regarded as 
not being true Lingulae. The term i Primordial,' first applied by M. Bar- 
rande to the base of the Silurian series in Bohemia, has thus been adopted 
as generally meaning the lowest Silurian zone, whether it be applied to 
the Alum-slates of Sweden and Norway, the Lingula-flags of Britain, or 
the Potsdam Sandstone of North America. 
In noticing the advances made in other countries, I have to acknowledge 
the more exact determination of Palaeozoic rocks in Spain by de Verneuil, 
the late Casiano de Prado, and M. Collomb, and of the older Palaeozoic 
rocks in Norway by the last researches of Kjerulf and Dahll ; also many 
contributions by de Verneuil, Barrande, Logan, Dawson, Helmersen, and 
other cotemporaries. 
In the Chapter on the origin of Gold in the crust of the globe, I have 
been furnished with new data as respects the two great auriferous regions 
of Australia and America — the former by Mr. Selwyn, and the latter by 
Mr. David Forbes. On this head, although I have had reason to modify 
a broad view put forth in former editions, yet I sustain the same leading- 
opinions as before concerning the origin of the noble metal, its main per- 
sistence in certain rocks, and its absence from all unaltered Secondary 
rocks. In some conglomeratic Tertiary deposits, however, formed out of 
auriferous Palaeozoic rocks, gold necessarily occurs, just as it does in more 
recent alluvia. 
* Eead before the Geological Society, April 1867. 
