ions, has furnished a solid foundation to climatology; while a
growing sense of the importance of the influence of the 'struggle for
existence' affords a wholesome check to the tendency to overrate the
influence of climate on distribution. Expeditions, such as that of the
Challenger,' equipped, not for geographical exploration and discovery,
but for the purpose of throwing light on problems of physical and
biological science, have been sent out by our own and other
Governments, and have obtained stores of information of the greatest
value. For the first time, we are in possession of something like
precise knowledge of the physical features of the deep seas, and of
the living population of the floor of the ocean. The careful and
exhaustive study of the phenomena presented by the accumulations of
snow and ice, in polar and mountainous regions, which has taken place
in our time, has not only revealed to the geologist an agent of
denudation and transport, which has slowly and quietly produced
effects, formerly confidently referred to diluvial catastrophes, but
it has suggested new methods of accounting for various puzzling facts
of distribution.

[Sidenote: Palaeontology.]

Palaeontology, which treats of the extinct forms of life and their
succession and distribution upon our globe, a branch of science which
could hardly be said to exist a century ago, has undergone a wonderful
development in our epoch. In some groups of animals and plants, the
extinct representatives, already known, are more numerous and
important than the living. There can be no doubt that the existing
Fauna and Flora is but the last term of a long series of equally
numerous contemporary species, which have succeeded one another, by
the slow and gradual substitution of species for species, in the vast
interval of time which has elapsed between the deposition of the
earliest fossiliferous strata and the present day. There is no
reasonable ground for believing that the oldest remains yet obtained
carry us even near the beginnings of life. The impressive warnings of
Lyell against hasty speculations, based upon negative evidence, have
been fully justified; time after time, highly organised types have
been discovered in formations of an age in which the existence of such
forms of life had been confidently declared to be impossible. The
western territories of the United States alone have yielded a world of
extinct animal forms, undreamed of fifty years ago. A