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 axiom, that like effects imply like causes. If there is any
cause competent to produce a fossil stem, or shell, or bone,