But, although palaeontology is a comparatively youthful
scientific speciality, the mass of materials with which it has
to deal is already prodigious. In the last fifty years the
number of known fossil remains of invertebrated animals has been
trebled or quadrupled. The work of interpretation of vertebrate
fossils, the foundations of which were so solidly laid by
Cuvier, was carried on, with wonderful vigour and success, by
Agassiz in Switzerland, by Von Meyer in Germany, and last, but
not least, by Owen in this country, while, in later years, a
multitude of workers have laboured in the same field. In many
groups of the animal kingdom the number of fossil forms already
known is as great as that of the existing species. In some cases
it is much greater; and there are entire orders of animals of
the existence of which we should know nothing except for the
evidence afforded by fossil remains. With all this it may be
safely assumed that, at the present moment, we are not
acquainted with a tittle of the fossils which will sooner or
later be discovered. If we may judge by the profusion yielded
within the last few years by the Tertiary formations of North
America, there seems to be no limit to the multitude of
mammalian remains to be expected from that continent;
and analogy leads us to expect similar riches in Eastern Asia,
whenever the Tertiary formations of that region are as carefully
explored. Again, we have, as yet, almost everything to learn
respecting the terrestrial population of the Mesozoic epoch;
and it seems as if the Western territories of the United States
were about to prove as instructive in regard to this point as
they have in respect of tertiary life. My friend Professor Marsh
informs me that, within two years, remains of more than 160