empts were made to explain this almost
unintelligible phenomenon upon the hypothesis that the fossils
in question were not really the objects they represented, but
were in truth mere _lusus naturoe_, due to some "plastic virtue
latent in the earth." The common-sense of scientific men, however,
soon rejected this idea, and it was agreed by universal consent
that these bodies really were remains of animals which formerly
lived in the sea. When once this was admitted, the further steps
were comparatively easy, and at the present day no geological
doctrine stands on a firmer basis than that which teaches us
that our present continents and islands, fixed and immovable as
they appear, have been repeatedly sunk beneath the ocean.

CHAPTER VI.

THE BIOLOGICAL RELATIONS OF FOSSILS.

Not only have fossils, as we have seen, a most important bearing
upon the sciences of Geology and Physical Geography, but they
have relations of the most complicated and weighty character with
the numerous problems connected with the study of living beings,
or in other words, with the science of Biology. To such an extent
is this the case, that no adequate comprehension of Zoology and
Botany, in their modern form, is so much as possible without
some acquaintance with the types of animals and plants which have
passed away. There are also numerous speculative questions in
the domain of vital science, which, if soluble at all, can only
hope to find their key in researches carried out on extinct
organisms. To discuss fully the biological relations of fossils
would, therefore, afford matter for a separate treatise; and all
that can be done here is to indicate very cursorily the principal
points to which the attention of the palaeontological student
ought to be directed.

In the first place, the great majority of fossil animals and
plants are "extinct"--that is to say, they belong to species
which are no longer in existence at the present day. So far,
however, from there being any truth in the old view that there
were periodic destructions of all the living beings in existence
upon the earth, followed by a corresponding number of new creations
of animals and plants, the actual facts of the case show that
the extinction of old forms and the introduction of new forms
have been processes constantly going on throughout the whole
of geological time. Every species seems to come into being at
a certain definite point of time, and to finally disappear