PREFACE.
IN revising this Edition, I have employed, as the
basis of classification for successive geological
periods, those great natural associations of the
forms of life which are expressed by the terms
Palæozoic, Mesozoic, and Cainozoic. In subdividing
the great classes of strata which were formed
in these successive "life-periods," no material
change has been found necessary, except in regard
to the Palæozoic formations. Among these a much
improved distribution has been effected, by labours
commenced in Britain, in 1831, by Murchison and
Sedgwick, and since extended by these and other
geologists over great part of the globe. If some of
the questions which these researches have raised
are as yet only provisionally answered, they are
placed in a form which may probably lead to sound
and comprehensive solutions. (Vol. I., Palæozoic Strata.)
Among the many objects of geological inquiry which have been successfully prosecuted of late years, the following must be distinguished:─
The beautiful structure of slate has acquired
