circumstance that the most important event in the history of
palaeontology which immediately succeeded William Smith's
generalisation was a discovery which, could it have been rightly
appreciated at the time, would have gone far towards suggesting
the answer, which was in fact delayed for more than half a
century. I refer to Cuvier's investigation of the mammalian
fossils yielded by the quarries in the older tertiary rocks of
Montmartre, among the chief results of which was the bringing to
light of two genera of extinct hoofed quadrupeds, the
Anoplotherium and the Palaeotherium. The rich
materials at Cuvier's disposition enabled him to obtain a full
knowledge of the osteology and of the dentition of these two
forms, and consequently to compare their structure critically
with that of existing hoofed animals. The effect of this
comparison was to prove that the Anoplotherium, though it
presented many points of resemblance with the pigs on the one
hand and with the ruminants on the other, differed from both to
such an extent that it could find a place in neither group.
In fact, it held, in some respects, an intermediate position,
tending to bridge over the interval between these two groups,
which in the existing fauna are so distinct. In the same way,
the Palaeotherium tended to connect forms so different as
the tapir, the rhinoceros, and the horse. Subsequent
investigations have brought to light a variety of facts of the
same order, the most curious and striking of which are those
which prove the existence, in the mesozoic epoch, of a series of
forms intermediate between birds and reptiles--two classes of
vertebrate animals which at present appear to be more widely
separated than any others. Yet the interval between them is
completely filled, in the mesozoic fauna, by birds which have