story, the latest forms are more modified, more specialised, than the
earlier. The fact that the dentition of the older tertiary ungulate
and carnivorous mammals is always complete, noticed by Professor Owen,
illustrated the same generalisation.

Another no less suggestive observation was made by Mr. Darwin, whose
personal investigations during the voyage of the _Beagle_ led him
to remark upon the singular fact, that the fauna, which immediately
precedes that at present existing in any geographical province of
distribution, presents the same peculiarities as its successor. Thus, in
South America and in Australia, the later tertiary or quaternary fossils
show that the fauna which immediately preceded that of the present day
was, in the one case, as much characterised by edentates and, in the
other, by marsupials as it is now, although the species of the older are
largely different from those of the newer fauna.

However clearly these indications might point in one direction, the
question of the exact relation of the successive forms of animal and
vegetable life could be satisfactorily settled only in one way; namely,
by comparing, stage by stage, the series of forms presented by one and
the same type throughout a long space of time. Within the last few years
this has been done fully in the case of the horse, less completely
in the case of the other principal types of the ungulata and of the
carnivora; and all these investigations tend to one general result,
namely, that, in any given series, the successive members of that series
present a gradually increasing specialisation of structure. That is to
say, if any such mammal at present existing has specially modified and
reduced limbs or dentition and complicated brain, its predecessors in
time show less and less modification and reduction in limbs and teeth
and a less highly developed brain. The labours of Gaudry, Marsh, and
Cope furnish abundant illustrations of this law from the marvellous
fossil wealth of Pikermi and the vast uninterrupted series of tertiary
rocks in the territories of North America.

I will now sum up the results of this sketch of the rise and progress
of palaeontology. The whole fabric of palaeontology is based upon two
propositions: the first is, that fossils are the remains of animals and
plants; and the second is, that the stratified rocks in which they
are found are sedimentary deposits; and each of these propositions is
founded upon the same ax