s. We may go
still farther back. I have already referred to the fact that the
Carboniferous formations, in Europe and in America, contain the remains
of scorpions in an admirable state of preservation, and that those
scorpions are hardly distinguishable from such as now live. I do not
mean to say that they are not different, but close scrutiny is needed in
order to distinguish them from modern scorpions.

More than this. At the very bottom of the Silurian series, in beds which
are by some authorities referred to the Cambrian formation, where the
signs of life begin to fail us--even there, among the few and scanty
animal remains which are discoverable, we find species of molluscous
animals which are so closely allied to existing forms that, at one time,
they were grouped under the same generic name. I refer to the well-known
_Lingula_ of the _Lingula_ flags, lately, in consequence of some slight
differences, placed in the new genus _Lingulella_. Practically, it
belongs to the same great generic group as the _Lingula_, which is to be
found at the present day upon your own shores and those of many other
parts of the world.

The same truth is exemplified if we turn to certain great periods of the
earth's history--as, for example, the Mesozoic epoch. There are groups
of reptiles, such as the _Ichthyosauria_ and the _Plesiosauria_, which
appear shortly after the commencement of this epoch, and they occur in
vast numbers. They disappear with the chalk and, throughout the whole of
the great series of Mesozoic rocks, they present no such modifications
as can safely be considered evidence of progressive modification.

Facts of this kind are undoubtedly fatal to any form of the doctrine of
evolution which postulates the supposition that there is an intrinsic
necessity, on the part of animal forms which have once come into
existence, to undergo continual modification; and they are as distinctly
opposed to any view which involves the belief, that such modification as
may occur, must take place, at the same rate, in all the different types
of animal or vegetable life. The facts, as I have placed them before
you, obviously directly contradict any form of the hypothesis of
evolution which stands in need of these two postulates.

But, one great service that has been rendered by Mr. Darwin to the
doctrine of evolution in general is this: he has shown that there are
two chief factors in the process of evolution: one of them is the
ten