e more, as
the considerations which have been laid before you have certainly
not tended to increase your estimation of such evidence. It will be
preferable to turn to the positive facts of paleontology, and to inquire
what they tell us.

We are all accustomed to speak of the number and the extent of the
changes in the living population of the globe during geological time
as something enormous: and indeed they are so, if we regard only the
negative differences which separate the older rocks from the more
modern, and if we look upon specific and generic changes as great
changes, which from one point of view, they truly are. But leaving
the negative differences out of consideration, and looking only at the
positive data furnished by the fossil world from a broader point of
view--from that of the comparative anatomist who has made the study of
the greater modifications of animal form his chief business--a surprise
of another kind dawns upon the mind; and under 'this' aspect the
smallness of the total change becomes as astonishing as was its
greatness under the other.

There are two hundred known orders of plants; of these not one is
certainly known to exist exclusively in the fossil state. The whole
lapse of geological time has as yet yielded not a single new ordinal
type of vegetable structure.* ([Footnote] *See Hooker's 'Introductory
Essay to the Flora of Tasmania', p. xxiii.)

The positive change in passing from the recent to the ancient animal
world is greater, but still singularly small. No fossil animal is so
distinct from those now living as to require to be arranged even in a
separate class from those which contain existing forms. It is only when
we come to the orders, which may be roughly estimated at about a hundred
and thirty, that we meet with fossil animals so distinct from those now
living as to require orders for themselves; and these do not amount, on
the most liberal estimate, to more than about 10 per cent of the whole.

There is no certainly known extinct order of Protozoa; there is but one
among the Coelenterata--that of the rugose corals; there is none
among the Mollusca; there are three, the Cystidea, Blastoidea, and
Edrioasterida, among the Echinoderms; and two, the Trilobita and
Eurypterida, among the Crustacea; making altogether five for the
great sub-kingdom of Annulosa. Among Vertebrates there is no ordinally
distinct fossil fish: there is only one extinct order of Amphibia--the
Labyrinthodon