rveyor,
whose business took him into many parts of England, profited by the
peculiarly favourable conditions offered by the arrangement of our
secondary strata to make a careful examination and comparison of their
fossil contents at different points of the large area over which they
extend. The result of his accurate and widely-extended observations
was to establish the important truth that each stratum contains certain
fossils which are peculiar to it; and that the order in which the
strata, characterised by these fossils, are super-imposed one upon the
other is always the same. This most important generalisation was
rapidly verified and extended to all parts of the world accessible to
geologists; and now it rests upon such an immense mass of observations
as to be one of the best established truths of natural science. To the
geologist the discovery was of infinite importance as it enabled him to
identify rocks of the same relative age, however their continuity might
be interrupted or their composition altered. But to the biologist it
had a still deeper meaning, for it demonstrated that, throughout the
prodigious duration of time registered by the fossiliferous rocks, the
living population of the earth had undergone continual changes, not
merely by the extinction of a certain number of the species which had at
first existed, but by the continual generation of new species, and the
no less constant extinction of old ones.

Thus the broad outlines of palaeontology, in so far as it is the common
property of both the geologist and the biologist, were marked out at
the close of the last century. In tracing its subsequent progress I must
confine myself to the province of biology, and, indeed, to the
influence of palaeontology upon zoological morphology. And I accept
this limitation the more willingly as the no less important topic of
the bearing of geology and of palaeontology upon distribution has been
luminously treated in the address of the President of the Geographical
Section. [3]

The succession of the species of animals and plants in time being
established, the first question which the zoologist or the botanist had
to ask himself was, What is the relation of these successive species
one to another? And it is a curious circumstance that the most important
event in the history of palaeontology which immediately succeeded
William Smith's generalisation was a discovery which, could it have been
rightly appreciated at the