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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
cases are examples of what I have designated negative or
indifferent evidencethat is to say； they in no way directly
advance the hypothesis of evolution； but they are not to be
regarded as obstacles in the way of our belief in that doctrine。
I now pass on to the consideration of those cases which； for
reasons which I will point out to you by and by； are not to be
regarded as demonstrative of the truth of evolution； but which
are such as must exist if evolution be true； and which therefore
are； upon the whole； evidence in favour of the doctrine。 If the
doctrine of evolution be true； it follows； that； however diverse
the different groups of animals and of plants may be； they must
all； at one time or other； have been connected by gradational
forms； so that； from the highest animals； whatever they may be；
down to the lowest speck of protoplasmic matter in which life
can be manifested； a series of gradations； leading from one end
of the series to the other； either exists or has existed。
Undoubtedly that is a necessary postulate of the doctrine of
evolution。 But when we look upon living Nature as it is； we find
a totally different state of things。 We find that animals and
plants fall into groups； the different members of which are
pretty closely allied together； but which are separated by
definite； larger or smaller； breaks； from other groups。 In other
words； no intermediate forms which bridge over these gaps or
intervals are； at present； to be met with。
To illustrate what I mean： Let me call your attention to those
vertebrate animals which are most familiar to you； such as
mammals； birds； and reptiles。 At the present day； these groups
of animals are perfectly well…defined from one another。 We know
of no animal now living which； in any sense； is intermediate
between the mammal and the bird； or between the bird and the
reptile； but； on the contrary； there are many very distinct
anatomical peculiarities； well…defined marks； by which the
mammal is separated from the bird； and the bird from the
reptile。 The distinctions are obvious and striking if you
compare the definitions of these great groups as they now exist。
The same may be said of many of the subordinate groups； or
orders； into which these great classes are divided。 At the
present time； for example； there are numerous forms of non…
ruminant pachyderms； or what we may call broadly； the pig tribe；
and many varieties of ruminants。 These latter have their
definite characteristics； and the former have their
distinguishing peculiarities。 But there is nothing that fills up
the gap between the ruminants and the pig tribe。 The two are
distinct。 Such also is the case in respect of the minor groups
of the class of reptiles。 The existing fauna shows us
crocodiles； lizards； snakes； and tortoises； but no connecting
link between the crocodile and lizard； nor between the lizard
and snake； nor between the snake and the crocodile； nor be