k differently of the
completeness of our knowledge by the next facts I shall state to you.

The researches of the last three-quarters of a century have, in truth,
revealed a wonderful richness of organic life in those rocks. Certainly
not fewer than thirty or forty thousand different species of fossils
have been discovered. You have no more ground for doubting that these
creatures really lived and died at or near the places in which we find
them than you have for like scepticism about a shell on the sea-shore.
The evidence is as good in the one case as in the other.

Our next business is to look at the general character of these fossil
remains, and it is a subject which it will be requisite to consider
carefully; and the first point for us is to examine how much the
extinct 'Flora' and 'Fauna' as a 'whole'--disregarding altogether
the 'succession' of their constituents, of which I shall speak
afterwards--differ from the 'Flora' and 'Fauna' of the present day;--how
far they differ in what we 'do' know about them, leaving altogether out
of consideration speculations based upon what we 'do not' know.

I strongly imagine that if it were not for the peculiar appearance that
fossilised animals have, any of you might readily walk through a museum
which contains fossil remains mixed up with those of the present forms
of life, and I doubt very much whether your uninstructed eyes would
lead you to see any vast or wonderful difference between the two. If
you looked closely, you would notice, in the first place, a great many
things very like animals with which you are acquainted now: you would
see differences of shape and proportion, but on the whole a close
similarity.

I explained what I meant by ORDERS the other day, when I described the
animal kingdom as being divided in sub-kingdoms, classes and orders. If
you divide the animal kingdom into orders, you will find that there are
about one hundred and twenty. The number may vary on one side or the
other, but this is a fair estimate. That is the sum total of the orders
of all the animals which we know now, and which have been known in past
times, and left remains behind.

Now, how many of those are absolutely extinct? That is to say, how many
of these orders of animals have lived at a former period of the world's
history, but have at present no representatives? That is the sense in
which I meant to use the word "extinct." I mean that those animals did
live on this earth at on