of which the most part belong to animals of those kinds which
still exist in southern seas, but of which many others have no
living analogues; so that these species appear to be lost,
destroyed by some unknown cause. It is needless to inquire how
far these statements are strictly accurate; they are
sufficiently so to justify Buffon's conclusions that the dry
land was once beneath the sea; that the formation of the
fossiliferous rocks must have occupied a vastly greater lapse of
time than that traditionally ascribed to the age of the earth;
that fossil remains indicate different climatal conditions to
have obtained in former times, and especially that the polar
regions were once warmer; that many species of animals and
plants have become extinct; and that geological change has had
something to do with geographical distribution.

But these propositions almost constitute the frame-work of
palaeontology. In order to complete it but one addition was
needed, and that was made, in the last years of the eighteenth
century, by William Smith, whose work comes so near our own
times that many living men may have been personally acquainted
with him. This modest land-surveyor, 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