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and； indeed； it has been determined that； when these animals
lived； the falls of Niagara must have been at least six miles
further down the river than they are at present。
Many computations have been made of the rate at which the falls
are thus cutting their way back。 Those computations have varied
greatly； but I believe I am speaking within the bounds of
prudence； if I assume that the falls of Niagara have not
retreated at a greater pace than about a foot a year。 Six miles；
speaking roughly； are 30；000 feet； 30；000 feet； at a foot a
year； gives 30；000 years； and thus we are fairly justified in
concluding that no less a period than this has passed since the
shell…fish； whose remains are left in the beds to which I have
referred； were living creatures。
But there is still stronger evidence of the long duration of
certain types。 I have already stated that； as we work our way
through the great series of the Tertiary formations； we find
many species of animals identical with those which live at the
present day； diminishing in numbers； it is true； but still
existing； in a certain proportion； in the oldest of the Tertiary
rocks。 Furthermore； when we examine the rocks of the Cretaceous
epoch； we find the remains of some animals which the closest
scrutiny cannot show to be； in any important respect； different
from those which live at the present time。 That is the case with
one of the cretaceous lamp…shells （Terebratula）； which
has continued to exist unchanged； or with insignificant
variations； down to the present day。 Such is the case with the
Globigerin？； the skeletons of which； aggregated together；
form a large proportion of our English chalk。
Those Globigerinae can be traced down to the
Globigerinae which live at the surface of the present
great oceans； and the remains of which； falling to the bottom of
the sea； give rise to a chalky mud。 Hence it must be admitted
that certain existing species of animals show no distinct sign
of modification； or transformation； in the course of a lapse of
time as great as that which carries us back to the Cretaceous
period； and which； whatever its absolute measure； is certainly
vastly greater than thirty thousand years。
There are groups of species so closely allied together； that it
needs the eye of a naturalist to distinguish them one from
another。 If we disregard the small differences which separate
these forms； and consider all the species of such groups as
modifications of one type； we shall find that； even among the
higher animals； some types have had a marvellous duration。
In the chalk； for example； there is found a fish belonging to
the highest and the most differentiated group of osseous fishes；
which goes by the name of Beryx。 The remains of that fish
are among the most beautiful and well…preserved of the fossils
found in our English chalk。 It can be studied anatomically； so
far as the hard parts are concerned； almost as well as if it
were a recent fish。 But the genus Beryx is represented；
at the present day； by very closely allied species which are
living in the Pacific and Atlantic Oceans。 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 useven 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 historyas； 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 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 tendency to vary； the existence of which in all
living forms may be proved by observation； the other is the
influence of surrounding conditions upon what I may call the
parent form and the variations which are thus evolved from it。
The cause of the production of variations is a matter not at all
properly understood at present。 Whether variation depends upon
some intricate machineryif I may use the phraseof the living
organism itself； or whether it arises through the influence of
conditions upon that form； is not certain； and the question may；
for the present； be left open。 But the important point is that；
granting the existence of the tendency to the production of
variations； then； whether the variations which are produced
shall survive and supplant the parent； or whether the parent
form shall survive and supplant the variations； is a matter
which depends entirely on those conditions which give rise to
the struggle for existence。 If the surrounding conditions are
such that the parent form is more competent to deal with them；
and flourish in them than the derived forms； then； in the
struggle for existence； the parent form will maintain itself and
the derived forms will be exterminated。 But if； on the contrary；
the conditions are such as to be more favourable to a derived
than to the parent form； the parent form will be extirpated and
the derived form will take its place。 In the first case； there
will be no progression； no change of structure； through any
imaginable series of ages； in the second place there will be
modification of change and form。
Thus the existence of these persistent types； as I have termed
them； is no real obstacle in the way of the theory of evolution。
Take the case of the scorpions to which I have just referred。
No doubt； since the Carboniferous epoch； conditions have always
obtained； such as existed when the scorpions of that epoch
flourished； conditions in which scorpions find themselves better
off； more competent to deal with the difficulties in their way；
than any variation from the scorpion type which they may have
produced； and； for that reason； the scorpion type has persisted；
and has not been supplanted by any other form。 And there is no
reason； in the nature of things； why； as long as this world
exists； if there be conditions more favourable to scorpions than
to any variation which may arise from them； these forms of life
should not persist。
Therefore； the stock objection to the hypothesis of evolution；
based on the long duration of certain animal and vegetable
types； is no objection at all。 The facts of this characterand
they are numerousbelong to that class of evidence which I have
called indifferent。 That is to say； they may afford no direct
support to the doctrine of evolution； but they are capable of
being interpreted in perfect consistency with it。
There is another order of facts belonging to the class of
negative or indifferent evidence。 The great group of Lizards；
which abound in the present world； extends through the whole
series of formations as far back as the Permian； or latest
Palaeozoic； epoch。 These Permian lizards differ astonishingly
little from the lizards which exist at the present day。
Comparing the amount of the differences bet