the successive formations.
Subject to these allowances, the fauna of each geological period
undoubtedly is intermediate in character, between the preceding and
succeeding faunas. I need give only one instance, namely, the manner
in which the fossils of the Devonian system, when this system was first
discovered, were at once recognised by palaeontologists as intermediate
in character between those of the overlying carboniferous, and
underlying Silurian system. But each fauna is not necessarily exactly
intermediate, as unequal intervals of time have elapsed between
consecutive formations.

It is no real objection to the truth of the statement, that the fauna of
each period as a whole is nearly intermediate in character between the
preceding and succeeding faunas, that certain genera offer exceptions
to the rule. For instance, mastodons and elephants, when arranged by Dr.
Falconer in two series, first according to their mutual affinities
and then according to their periods of existence, do not accord in
arrangement. The species extreme in character are not the oldest, or
the most recent; nor are those which are intermediate in character,
intermediate in age. But supposing for an instant, in this and other
such cases, that the record of the first appearance and disappearance
of the species was perfect, we have no reason to believe that forms
successively produced necessarily endure for corresponding lengths of
time: a very ancient form might occasionally last much longer than
a form elsewhere subsequently produced, especially in the case of
terrestrial productions inhabiting separated districts. To compare small
things with great: if the principal living and extinct races of the
domestic pigeon were arranged as well as they could be in serial
affinity, this arrangement would not closely accord with the order
in time of their production, and still less with the order of their
disappearance; for the parent rock-pigeon now lives; and many varieties
between the rock-pigeon and the carrier have become extinct; and
carriers which are extreme in the important character of length of beak
originated earlier than short-beaked tumblers, which are at the opposite
end of the series in this same respect.

Closely connected with the statement, that the organic remains from an
intermediate formation are in some degree intermediate in character,
is the fact, insisted on by all palaeontologists, that fossils from two
consecutive formation