P E E 1 A C E. 
The term ' Silurian,' when first applied by me in 1835 (and in my large 
work, entitled the ' Silurian System,' completed in 1838), was intended to 
characterize a great natural system of ancient deposits which had not 
before been classified, and the type of which was found to be exhibited in 
Siluria, or the country of Caractacus and the old Britons known as 
' Silures.' The name of 6 Siluria ' has also been given to the preceding 
and present editions of this volume, descriptive not only of the Silurian 
rocks, but all the Palaeozoic deposits, from the earliest in which traces of 
life have been discovered. The important additions made to our knowledge 
respecting these ancient deposits within the last eight years have induced 
me to prepare this new edition, in which, by the use of a smaller type, a 
great amount of new matter has been included without increasing the size 
of the volume. 
The most important of these additions is the discovery, made by Logan 
and his associates in British North America, of an organic body in the old 
gneissic Laurentian or bottom -rocks of that region. The existence of 
these, the most ancient of all stratified deposits, beneath the Cambrian and 
Lower Silurian rocks of the North-west of Scotland, as first proved by my 
own labours, was announced in the last edition, when it was illustrated by 
the coloured Frontispiece now reproduced. 
The early portion of this volume has been enriched by knowledge 
derived from Professor Eamsay's work on the Geology of North Wales, 
wherein that author and his associates of the Geological Survey have, after 
long and skilful researches, most successfully developed the details and 
structure of the most complicated and diversified of all the Silurian tracts 
of Britain. In the same volume Mr. Salter, who aided me so essentially 
in bringing out the earlier editions of ' Siluria,' has, with his recognized 
ability, described several new species, the position of many of which he 
had noted in situ. 
The very remarkable work by Mr. Thomas Davidson on the Silurian 
Brachiopoda of Britain, the result, like several other of his publications, 
of many years of matured aud critical study and comparison, has already" 
