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I must ask you to believe that there is no less conclusive proof
that a still more prolonged succession of similar changes occurred；
before the chalk was deposited。 Nor have we any reason to think
that the first term in the series of these changes is known。 The
oldest sea…beds preserved to us are sands； and mud； and pebbles；
the wear and tear of rocks which were formed in still older oceans。
But； great as is the magnitude of these physical changes of the
world； they have been accompanied by a no less striking series of
modifications in its living inhabitants。
All the great classes of animals； beasts of the field； fowls of the
air； creeping things； and things which dwell in the waters；
flourished upon the globe long ages before the chalk was deposited。
Very few； however； if any； of these ancient forms of animal life
were identical with those which now live。 Certainly not one of the
higher animals was of the same species as any of those now in
existence。 The beasts of the field； in the days before the chalk；
were not our beasts of the field； nor the fowls of the air such as
those which the eye of men has seen flying； unless his antiquity
dates infinitely further back than we at present surmise。 If we
could be carried back into those times； we should be as one
suddenly set down in Australia before it was colonized。 We should
see mammals； birds； reptiles； fishes； insects； snails； and the
like； clearly recognisable as such； and yet not one of them would
be just the same as those with which we are familiar； and many
would be extremely different。
From that time to the present； the population of the world has
undergone slow and gradual； but incessant changes。 There has been
no grand catastropheno destroyer has swept away the forms of life
of one period； and replaced them by a totally new creation； but one
species has vanished and another has taken its place； creatures of
one type of structure have diminished； those of another have
increased； as time has passed on。 And thus； while the differences
between the living creatures of the time before the chalk and those
of the present day appear startling； if placed side by side； we are
led from one to the other by the most gradual progress； if we
follow the course of Nature through the whole series of those
relics of her operations which she has left behind。
And it is by the population of the chalk sea that the ancient and
the modern inhabitants of the world are most completely connected。
The groups which are dying out flourish； side by side； with the
groups which are now the dominant forms of life。
Thus the chalk contains remains of those strange flying and
swimming reptiles； the pterodactyl； the ichthyosaurus； and the
plesiosaurus； which are found in no later deposits； but abounded in
preceding ages。 The chambered shells called ammonites and
belemnites； which are so characteristic of the period preceding the
cretaceous； in like manner die with it。
But； amongst these fading remainders of a previous state of things；
are some very modern forms of life； looking like Yankee pedlars
among a tribe of Red Indians。 Crocodiles of modern type appear；
bony fishes； many of them very similar to existing species almost
supplant the forms of fish which predominate in more ancient seas；
and many kinds of living shellfish first become known to us in the
chalk。 The vegetation acquires a modern aspect。 A few living
animals are not even distinguishable as species； from those which
existed at that remote epoch。 The Globigerina of the present day；
for example； is not different specifically from that of the chalk；
and the same may be said of many other Foraminifera。 I think it
probable that critical and unprejudiced examination will show that
more than one species of much higher animals have had a similar
longevity； but the only example； which I can at present give
confidently is the snake's…head lamp…shell （Terebratulina caput
serpentis）； which lives in our English seas and abounded （as
Terebratulina striata of authors） in the chalk。
The longest line of human ancestry must hide its diminished head
before the pedigree of this insignificant shell…fish。 We
Englishmen are proud to have an ancestor who was present at the
Battle of Hastings。 The ancestors of Terebratulina caput serpentis
may have been present at a battle of Ichthyosauria in that part of
the sea which； when the chalk was forming； flowed over the site of
Hastings。 While all around has changed； this Terebratulina has
peacefully propagated its species from generation to generation；
and stands to this day； as a living testimony to the continuity of
the present with the past history of the globe。
Up to this moment I have stated； so far as I know； nothing but
well…authenticated facts； and the immediate conclusions which they
force upon the mind。
But the mind is so constituted that it does not willingly rest in
facts and immediate causes； but seeks always after a knowledge of
the remoter links in the chain of causation。
Taking the many changes of any given spot of the earth's surface；
from sea to land and from land to sea； as an established fact； we
cannot refrain from asking ourselves how these changes have
occurred。 And when we have explained themas they must be
explainedby the alternate slow movements of elevation and
depression which have affected the crust of the earth； we go still
further back； and ask； Why these movements？
I am not certain that any one can give you a satisfactory answer to
that question。 Assuredly I cannot。 All that can be said； for
certain； is； that such movements are part of the ordinary course of
nature； inasmuch as they are going on at the present time。 Direct
proof may be given； that some parts of the land of the northern
hemisphere are at this moment insensibly rising and others
insensibly sinking； and there is indirect； but perfectly
satisfactory； proof； that an enormous area now covered by the
Pacific has been deepened thousands of feet； since the present
inhabitants of that sea came into existence。
Thus there is not a shadow of a reason for believing that the
physical changes of the globe； in past times have been effected by
other than natural causes。
Is there any more reason for believing that the concomitant
modifications in the forms of the living inhabitants of the globe
have been brought about in other ways？
Before attempting to answer this question； let us try to form a
distinct mental picture of what has happened； in some special case。
The crocodiles are animals which； as a group； have a very vast
antiquity。 They abounded ages before the chalk was deposited； they
throng the rivers in warm climates； at the present day。 There is a
difference in the form of the joints of the back…bone； and in some
minor particulars； between the crocodiles of the present epoch and
those which lived before the chalk； but in the cretaceous epoch； as
I have already mentioned； the crocodiles had assumed the modern
type of structure。 Notwithstanding this； the crocodiles of the
chalk are not identically the same as those which lived in the
times called 〃older tertiary；〃 which succeeded the cretaceous
epoch； and the crocodiles of the older tertiaries are not identical
with those of the newer tertiaries； nor are these identical with
existing forms。 I leave open the question whether particular
species may have lived on from epoch to epoch。 But each epoch has
had its peculiar crocodiles； though all； since the chalk； have
belonged to the modern type； and differ simply in their
proportions； and in such structural particulars as are discernible
only to trained eyes。
How is the existence of this long succession of different species
of crocodiles to be accounted for？
Only two suppositions seem to be open to usEither each species of
crocodile has been specially created； or it has arisen out of some
pre…existing form by the operation of natural causes。
Choose your hypothesis； I have chosen mine。 I can find no warranty
for believing in the distinct creation of a score of successive
species of crocodiles in the course of countless ages of time。
Science gives no countenance to such a wild fancy； nor can even the
perverse ingenuity of a commentator pretend to discover this sense；
in the simple words in which the writer of Genesis records the
proceedings of the fifth and sixth days of the Creation。
On the other hand； I see no good reason for doubting the necessary
alternative； that all these varied species have been evolved from
pre…existing crocodilian forms； by the operation of causes as
completely a part of the common order of nature； as those which
have effected the changes of the inorganic world。
Few will venture to affirm that the reasoning which applies to
crocodiles loses its force among other animals； or among plants。
If one series of spe