an geologists have, at last,
succumbed to the weighty evidence which M. Barrande has accumulated,
and have admitted the doctrine of colonies. But the admission of the
doctrine of colonies implies the further admission that even identity
of organic remains is no proof of the synchronism of the deposits
which contain them.

4. The discussions touching the _Eozoon_, which commenced in 1864,
have abundantly justified the fourth proposition. In 1862, the oldest
record of life was in the Cambrian rocks; but if the _Eozoon_ be,
as Principal Dawson and Dr. Carpenter have shown so much reason for
believing, the remains of a living being, the discovery of its true
nature carried life back to a period which, as Sir William Logan has
observed, is as remote from that during which the Cambrian rocks were
deposited, as the Cambrian epoch itself is from the tertiaries. In
other words, the ascertained duration of life upon the globe was
nearly doubled at a stroke.

5. The significance of persistent types, and of the small amount of
change which has taken place even in those forms which can be shown to
have been modified, becomes greater and greater in my eyes, the longer
I occupy myself with the biology of the past.

Consider how long a time has elapsed since the Miocene epoch. Yet, at
that time, there is reason to believe that every important group in
every order of the _Mammalia_ was represented. Even the comparatively
scanty Eocene fauna yields examples of the orders _Cheiroptera,
Insectivora, Rodentia_, and _Perissodactyla_; of _Artiodactyla_
under both the Ruminant and the Porcine modifications; of _Carnivora,
Cetacea_, and _Marsupialia_.

Or, if we go back to the older half of the Mesozoic epoch, how truly
surprising it is to find every order of the _Reptilia_, except
the _Ophidia_, represented; while some groups, such as the
_Ornithoscelida_ and the _Pterosauria_, more specialized than any
which now exist, abounded.

There is one division of the _Amphibia_ which offers especially
important evidence upon this point, inasmuch as it bridges over the
gap between the Mesozoic and the Palaeozoic formations (often supposed
to be of such prodigious magnitude), extending, as it does, from the
bottom of the Carboniferous series to the top of the Trias, if not
into the Lias. I refer to the Labyrinthodonts. As the address of 1862
was passing through the press, I was able to mention, in a note, the
discovery of a large Labyrinthodont,