PREFACE.
 

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
Siluna, or the country of Caractacus and the old Britons known as
* Silures.' The name of ' 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 aU stratified deposits, beneath the Cambrian and
Lower Silurian rocks of the JS'orth-west of Scotland, as first proved by my
own labours, was announced in the last edition, when it was illustrated by
the coloured Prontispiece now reproduced.

The early portion of this volume has been enriched by knowledge
derived from Professor Ramsay's work on the Geology of IS'orth 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 compKcated 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
abihty, 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 and critical study and comparison, has already