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 between them and modern
lizards； with the prodigious lapse of time between the Permian
epoch and the present day； it may be said that the amount of
change is insignificant。 But； when we carry our researches
farther back in time； we find no trace of lizards； nor of any
true reptile whatever； in the whole mass of formations beneath
the Permian。
Now； it is perfectly clear that if our palaeontological
collections are to be taken； even approximately； as an adequate
representation of all the forms of animals and plants that have
ever lived； and if the record furnished by the known series of
beds of stratified rock covers the whole series of events which
constitute the history of life on the globe； such a fact as this
directly contravenes the hypothesis of evolution； because this
hypothesis postulates that the existence of every form must have
been preceded by that of some form little different from it。
Here； however； we have to take into consideration that important
truth so well insisted upon by Lyell and by Darwinthe
imperfection of the geological record。 It can be demonstrated
that the geological record must be incomplete； that it can only
preserve remains found in certain favourable localities and
under particular conditions； that it must be destroyed by
processes of denudation； and obliterated by processes of
metamorphosis。 Beds of rock of any thickness crammed full of
organic remains； may yet； either by the percolation of water
through them； or by the influence of subterranean heat； lose all
trace of these remains； and present the appearance of beds of
rock formed under conditions in which living forms were absent。
Such metamorphic rocks occur in formations of all ages； and； in
various cases； there are very good grounds for the belief that
they have contained organic remains； and that those remains have
been absolutely obliterated。
I insist upon the defects of the geological record the more
because those who have not attended to these matters are apt to
say； 〃It is all very well； but； when you get into a difficulty
with your theory of evolution； you appeal to the incompleteness
and the imperfection of the geological record；〃 and I want to
make it perfectly clear to you that this imperfection is a great
fact； which must be taken into account in all our speculations；
or we shall constantly be going wrong。
You see the singular series of footmarks； drawn of its natural
size in the large diagram hanging up here （Fig。 2）； which I owe
to the kindness of my friend Professor Marsh； with whom I had
the opportunity recently of visiting the precise locality in
Massachusetts in which these tracks occur。 I am； therefore； able
to give you my own testimony； if needed； that the diagram
accurately represents what we saw。 The valley of the Connecticut
is classical ground for the geologist。 It contains great beds of
sandstone； covering many square miles； which have evidently
formed a part of an ancient sea…shore； or； it may be； lake…
shore。 For a certain period of time after their deposition；
these beds have remained sufficiently soft to receive the
impressions of the feet of whatever animals walked over them；
and to preserve them afterwards； in exactly the same way as such
impressions are at this hour preserved on the shores of the Bay
of Fundy and elsewhere。 The diagram represents the track of some
gigantic animal； which walked on its hind legs。 You see the
series of marks made alternately by the right and by the left
foot； so that； from one impression to the other of the three…
toed foot on the same side； is one stride； and that stride； as
we measured it； is six feet nine inches。 I leave you； therefore；
to form an impression of the magnitude of the creature which； as
it walked along the ancient shore； made these impressions。
Fig。 2。Tracks of Brontozoum。
Of such impressions there are untold thousands upon these
sandstones。 Fifty or sixty different kinds have been discovered；
and they cover vast areas。 But； up to this present time； not a
bone； not a fragment； of any one of the animals which left these
great footmarks has been found； in fact； the only animal remains
which have been met with in all these deposits； from the time of
their discovery to the present daythough they have been
carefully hunted overis a fragmentary skeleton of one of the
smaller forms。 What has become of the bones of all these
animals？ You see we are not dealing with little creatures； but
with animals that make a step of six feet nine inches； and their
remains must have been left somewhere。 The probability is； that
they have been dissolved away； and completely lost。
I have had occasion to work out the nature of fossil remains； of
which there was nothing left except casts of the bones； the
solid material of the skeleton having been dissolved out by
percolating water。 It was a chance； in this case； that the
sandstone happened to be of such a constitution as to set； and
to allow the bones to be afterward dissolved out； leaving
cavities of the exact shape of the bones。 Had that constitution
been other than what it was； the bones would have been
dissolved； the layers of sandstone would have fallen together
into one mass； and not the slightest indication that the animal
had existed would have been discoverable。
I know of no more striking evidence than these facts afford； of
the caution which should be used in drawing the conclusion； from
the absence of organic remains in a deposit； that animals or
plants did not exist at the time it was formed。 I believe that；
with a right understanding of the doctrine of evolution on the
one hand； and a just estimation of the importance of the
imperfection of the geological record on the other； all
difficulty is removed from the kind of evidence to which I have
adverted； and that we are justified in believing that all such