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Title: The Past Condition of Organic Nature
Lecture II. (of VI.), Lectures To Working Men, at the
Museum of Practical Geology, 1863, On Darwin's work: "Origin
of Species".
Author: Thomas H. Huxley
Posting Date: January 4, 2009 [EBook #2922]
Release Date: November, 2001
Language: English
*** START OF THIS PROJECT GUTENBERG EBOOK CONDITION OF ORGANIC NATURE ***
Produced by Amy E. Zelmer
THE PAST CONDITION OF ORGANIC NATURE
Lecture II. (of VI.), Lectures To Working Men, at the Museum of
Practical Geology, 1863, On Darwin's work: "Origin of Species".
by Thomas H. Huxley
IN the lecture which I delivered last Monday evening, I endeavoured to
sketch in a very brief manner, but as well as the time at my disposal
would permit, the present condition of organic nature, meaning by
that large title simply an indication of the great, broad, and general
principles which are to be discovered by those who look attentively at
the phenomena of organic nature as at present displayed. The general
result of our investigations might be summed up thus: we found that the
multiplicity of the forms of animal life, great as that may be, may be
reduced to a comparatively few primitive plans or types of construction;
that a further study of the development of those different forms
revealed to us that they were again reducible, until we at last brought
the infinite diversity of animal, and even vegetable life, down to the
primordial form of a single cell.
We found that our analysis of the organic world, whether animals or
plants, showed, in the long run, that they might both be reduced into,
and were, in fact, composed of, the same constituents. And we saw
that the plant obtained the materials constituting its substance by
a peculiar combination of matters belonging entirely to the inorganic
world; that, then, the animal was constantly appropriating the
nitrogenous matters of the plant to its own nourishment, and returning
them back to the inorganic world, in what we spoke of as its waste; and
that finally, when the animal ceased to exist, the constituents of its
body were dissolved and transmitted to that inorganic world whence they
had been at first abstracted. Thus we saw in both the blade of grass and
the horse but the same elements differently combined and arranged. We
discovered a continual circulation going on,--the plant drawing in the
elements of inorganic nature and combining them into food for the animal
creation; the animal borrowing from the plant the matter for its own
support, giving off during its life products which returned immediately
to the inorganic world; and that, eventually, the constituent materials
of the whole structure of both animals and plants were thus returned to
their original source: there was a constant passage from one state of
existence to another, and a returning back again.
Lastly, when we endeavoured to form some notion of the nature of the
forces exercised by living beings, we discovered that they--if
not capable of being subjected to the same minute analysis as the
constituents of those beings themselves--that they were correlative
with--that they were the equivalents of the forces of inorganic
nature--that they were, in the sense in which the term is now used,
convertible with them. That was our general result.
And now, leaving the Present, I must endeavour in the same manner to put
before you the facts that are to be discovered in the Past history of
the living world, in the past conditions of organic nature. We have,
to-night, to deal with the facts of that history--a history involving
periods of time before which our mere human records sink into utter
insignificance--a history the variety and physical magnitude of whose
events cannot even be foreshadowed by the history of human life and
human phenomena--a history of the most varied and complex character.
We must deal with the history, then, in the first place, as we should
deal with all other histories. The historical student knows that his
first business should be to inquire into the validity of his evidence,
and the nature of the record in which the evidence is contained, that
he may be able to form a proper estimate of the correctness of the
conclusions which have been drawn from that evidence. So, here, we must
pass, in the first place, to the consideration of a matter which may
seem foreign to the question under discussion. We must dwell upon the
nature of the records, and the credibility of the evidence they contain;
we must look to the completeness or incompleteness of those records
themselves, before we turn to that which they contain and reveal. The
question of the credibility of the history, happily for us, will not
require much consideration, for, in this history, unlike those of human
origin, there can be no cavilling, no differences as to the reality and
truth of the facts of which it is made up; the facts state themselves,
and are laid out clearly before us.
But, although one of the greatest difficulties of the historical student
is cleared out of our path, there are other difficulties--difficulties
in rightly interpreting the facts as they are presented to us--which
may be compared with the greatest difficulties of any other kinds of
historical study.
What is this record of the past history of the globe, and what are the
questions which are involved in an inquiry into its completeness or
incompleteness? That record is composed of mud; and the question which
we have to investigate this evening resolves itself into a question
of the formation of mud. You may think, perhaps, that this is a
vast step--of almost from the sublime to the ridiculous--from the
contemplation of the history of the past ages of the world's existence
to the consideration of the history of the formation of mud! But,
in nature, there is nothing mean and unworthy of attention; there
is nothing ridiculous or contemptible in any of her works; and this
inquiry, you will soon see, I hope, takes us to the very root and
foundations of our subject.
How, then, is mud formed? Always, with some trifling exception, which
I need not consider now--always, as the result of the action of water,
wearing down and disintegrating the surface of the earth and rocks with
which it comes in contact--pounding and grinding it down, and carrying
the particles away to places where they cease to be disturbed by this
mechanical action, and where they can subside and rest. For the ocean,
urged by winds, washes, as we know, a long extent of coast, and every
wave, loaded as it is with particles of sand and gravel as it breaks
upon the shore, does something towards the disintegrating process. And
thus, slowly but surely, the hardest rocks are gradually ground down to
a powdery substance; and the mud thus formed, coarser or finer, as the
case may be, is carried by the rush of the tides, or currents, till it
reaches the comparatively deeper parts of the ocean, in which it can
sink to the bottom, that is, to parts where there is a depth of about
fourteen or fifteen fathoms, a depth at which the water is, usually,
nearly motionless, and in which, of course, the finer particles of this
detritus, or mud as we call it, sinks to the bottom.
Or, again, if you take a river, rushing down from its mountain sources,
brawling over the stones and rocks that intersect its path, loosening,
removing, and carrying with it in its downward course the pebbles and
lighter matters from its banks, it crushes and pounds down the rocks and
earths in precisely the same way as the wearing action of the sea waves.
The matters forming the deposit are torn from the mountain-side and
whirled impetuously into the valley, more slowly over the plain, thence
into the estuary, and from the estuary they are swept into the sea. The
coarser and heavier fragments are obviously deposited first, that is,
as soon as the current begins to lose its force by becoming amalgamated
with the stiller depths of the ocean, but the finer and lighter
particles are carried further on, and eventually deposited in a deeper
and stiller portion of the ocean.
It clearly follows from this that mud gives us a chronology; for it is
evident that supposing this, which I now sketch, to be the sea bottom,
and supposing this to be a coast-line; from the washing action of the
sea upon the rock, wearing and grinding it down into a sediment of mud,
the mud will be carried down, and at length, deposited in the deeper
parts of this sea bottom, where it will form a layer; and then, while
that first layer is hardening, other mud which is coming from the same
source will, of course, be carried to the same place; and, as it is
quite impossible for it to get beneath the layer already there, it
deposits itself above it, and forms another layer, and in that way you
gradually have layers of mud constantly forming and hardening one above
the other, and conveying a record of time.
It is a necessary result of the operation of the law of gravitation that
the uppermost layer shall be the youngest and the lowest the oldest, and
that the different beds shall be older at any particular point or spot
in exactly the ratio of their depth from the surface. So that if they
were upheaved afterwards, and you had a series of these different layers
of mud, converted into sandstone, or limestone, as the case might be,
you might be sure that the bottom layer was deposited first, and that
the upper layers were formed afterwards. Here, you see, is the first
step in the history--these layers of mud give us an idea of time.
The whole surface of the earth,--I speak broadly, and leave out minor
qualifications,--is made up of such layers of mud, so hard, the majority
of them, that we call them rock whether limestone or sandstone, or other
varieties of rock. And, seeing that every part of the crust of the earth
is made up in this way, you might think that the determination of the
chronology, the fixing of the time which it has taken to form this crust
is a comparatively simple matter. Take a broad average, ascertain how
fast the mud is deposited upon the bottom of the sea, or in the estuary
of rivers; take it to be an inch, or two, or three inches a year, or
whatever you may roughly estimate it at; then take the total thickness
of the whole series of stratified rocks, which geologists estimate at
twelve or thirteen miles, or about seventy thousand feet, make a sum
in short division, divide the total thickness by that of the quantity
deposited in one year, and the result will, of course, give you the
number of years which the crust has taken to form.
Truly, that looks a very simple process! It would be so except for
certain difficulties, the very first of which is that of finding how
rapidly sediments are deposited; but the main difficulty--a difficulty
which renders any certain calculations of such a matter out of the
question--is this, the sea-bottom on which the deposit takes place is
continually shifting.
Instead of the surface of the earth being that stable, fixed thing that
it is popularly believed to be, being, in common parlance, the very
emblem of fixity itself, it is incessantly moving, and is, in fact,
as unstable as the surface of the sea, except that its undulations are
infinitely slower and enormously higher and deeper.
Now, what is the effect of this oscillation? Take the case to which
I have previously referred. The finer or coarser sediments that are
carried down by the current of the river, will only be carried out a
certain distance, and eventually, as we have already seen, on reaching
the stiller part of the ocean, will be deposited at the bottom.
Let C y (Fig. 4) be the sea-bottom, y D the shore, x y the sea-level,
then the coarser deposit will subside over the region B, the finer over
A, while beyond A there will be no deposit at all; and, consequently, no
record will be kept, simply because no deposit is going on. Now, suppose
that the whole land, C, D, which we have regarded as stationary, goes
down, as it does so, both A and B go further out from the shore, which
will be at y1; x1, y1, being the new sea-level. The consequence will be
that the layer of mud (A), being now, for the most part, further than
the force of the current is strong enough to convey even the finest
'debris', will, of course, receive no more deposits, and having attained
a certain thickness will now grow no thicker.
We should be misled in taking the thickness of that layer, whenever it
may be exposed to our view, as a record of time in the manner in which
we are now regarding this subject, as it would give us only an imperfect
and partial record: it would seem to represent too short a period of
time.
[Illustration: Fig.4.]
Suppose, on the other hand, that the land (C D) had gone on rising
slowly and gradually--say an inch or two inches in the course of a
century,--what would be the practical effect of that movement? Why, that
the sediment A and B which has been already deposited, would eventually
be brought nearer to the shore-level, and again subjected to the wear
and tear of the sea; and directly the sea begins to act upon it, it
would of course soon cut up and carry it away, to a greater or less
extent, to be re-deposited further out.
Well, as there is, in all probability, not one single spot on the whole
surface of the earth, which has not been up and down in this way a great
many times, it follows that the thickness of the deposits formed at any
particular spot cannot be taken (even supposing we had at first obtained
correct data as to the rate at which they took place) as affording
reliable information as to the period of time occupied in its deposit.
So that you see it is absolutely necessary from these facts, seeing that
our record entirely consists of accumulations of mud, superimposed one
on the other; seeing in the next place that any particular spots on
which accumulations have occurred, have been constantly moving up and
down, and sometimes out of the reach of a deposit, and at other times
its own deposit broken up and carried away, it follows that our record
must be in the highest degree imperfect, and we have hardly a trace
left of thick deposits, or any definite knowledge of the area that they
occupied, in a great many cases. And mark this! That supposing even
that the whole surface of the earth had been accessible to the
geologist,--that man had had access to every part of the earth, and had
made sections of the whole, and put them all together,--even then his
record must of necessity be imperfect.
But to how much has man really access? If you will look at this Map you
will see that it represents the proportion of the sea to the earth: this
coloured part indicates all the dry land, and this other portion is the
water. You will notice at once that the water covers three-fifths of the
whole surface of the globe, and has covered it in the same manner ever
since man has kept any record of his own observations, to say nothing of
the minute period during which he has cultivated geological inquiry.
So that three-fifths of the surface of the earth is shut out from us
because it is under the sea. Let us look at the other two-fifths,
and see what are the countries in which anything that may be termed
searching geological inquiry has been carried out: a good deal of
France, Germany, and Great Britain and Ireland, bits of Spain, of
Italy, and of Russia, have been examined, but of the whole great mass of
Africa, except parts of the southern extremity, we know next to nothing;
little bits of India, but of the greater part of the Asiatic continent
nothing; bits of the Northern American States and of Canada, but of
the greater part of the continent of North America, and in still larger
proportion, of South America, nothing!
Under these circumstances, it follows that even with reference to that
kind of imperfect information which we can possess, it is only of about
the ten-thousandth part of the accessible parts of the earth that has
been examined properly. Therefore, it is with justice that the most
thoughtful of those who are concerned in these inquiries insist
continually upon the imperfection of the geological record; for, I
repeat, it is absolutely necessary, from the nature of things, that
that record should be of the most fragmentary and imperfect character.
Unfortunately this circumstance has been constantly forgotten. Men of
science, like young colts in a fresh pasture, are apt to be exhilarated
on being turned into a new field of inquiry, to go off at a hand-gallop,
in total disregard of hedges and ditches, losing sight of the real
limitation of their inquiries, and to forget the extreme imperfection of
what is really known. Geologists have imagined that they could tell us
what was going on at all parts of the earth's surface during a given
epoch; they have talked of this deposit being contemporaneous with
that deposit, until, from our little local histories of the changes at
limited spots of the earth's surface, they have constructed a universal
history of the globe as full of wonders and portents as any other story
of antiquity.
But what does this attempt to construct a universal history of the globe
imply? It implies that we shall not only have a precise knowledge of the
events which have occurred at any particular point, but that we shall
be able to say what events, at any one spot, took place at the same time
with those at other spots.
Let us see how far that is in the nature of things practicable. Suppose
that here I make a section of the Lake of Killarney, and here the
section of another lake--that of Loch Lomond in Scotland for instance.
The rivers that flow into them are constantly carrying down deposits of
mud, and beds, or strata, are being as constantly formed, one above the
other, at the bottom of those lakes. Now, there is not a shadow of
doubt that in these two lakes the lower beds are all older than the
upper--there is no doubt about that; but what does 'this' tell us about
the age of any given bed in Loch Lomond, as compared with that of any
given bed in the Lake of Killarney? It is, indeed, obvious that if
any two sets of deposits are separated and discontinuous, there is
absolutely no means whatever given you by the nature of the deposit of
saying whether one is much younger or older than the other; but you may
say, as many have said and think, that the case is very much altered if
the beds which we are comparing are continuous. Suppose two beds of mud
hardened into rock,--A and B-are seen in section. (Fig. 5.)
[Illustration: Fig. 5.]
Well, you say, it is admitted that the lowermost bed is always the
older. Very well; B, therefore, is older than A. No doubt, 'as a whole',
it is so; or if any parts of the two beds which are in the same vertical
line are compared, it is so. But suppose you take what seems a very
natural step further, and say that the part 'a' of the bed A is younger
than the part 'b' of the bed B. Is this sound reasoning? If you find any
record of changes taking place at 'b', did they occur before any events
which took place while 'a' was being deposited? It looks all very plain
sailing, indeed, to say that they did; and yet there is no proof of
anything of the kind. As the former Director of this Institution, Sir
H. De la Beche, long ago showed, this reasoning may involve an entire
fallacy. It is extremely possible that 'a' may have been deposited ages
before 'b'. It is very easy to understand how that can be. To return
to Fig. 4; when A and B were deposited, they were 'substantially'
contemporaneous; A being simply the finer deposit, and B the coarser
of the same detritus or waste of land. Now suppose that that sea-bottom
goes down (as shown in Fig. 4), so that the first deposit is carried
no farther than 'a', forming the bed Al, and the coarse no farther
than 'b', forming the bed B1, the result will be the formation of two
continuous beds, one of fine sediment (A A1) over-lapping another of
coarse sediment (B B1). Now suppose the whole sea-bottom is raised up,
and a section exposed about the point Al; no doubt, 'at this spot', the
upper bed is younger than the lower. But we should obviously greatly err
if we concluded that the mass of the upper bed at A was younger than
the lower bed at B; for we have just seen that they are contemporaneous
deposits. Still more should we be in error if we supposed the upper bed
at A to be younger than the continuation of the lower bed at Bl; for
A was deposited long before B1. In fine, if, instead of comparing
immediately adjacent parts of two beds, one of which lies upon another,
we compare distant parts, it is quite possible that the upper may be any
number of years older than the under, and the under any number of years
younger than the upper.
Now you must not suppose that I put this before you for the purpose of
raising a paradoxical difficulty; the fact is, that the great mass of
deposits have taken place in sea-bottoms which are gradually sinking,
and have been formed under the very conditions I am here supposing.
Do not run away with the notion that this subverts the principle I
laid down at first. The error lies in extending a principle which is
perfectly applicable to deposits in the same vertical line to deposits
which are not in that relation to one another.
It is in consequence of circumstances of this kind, and of others that I
might mention to you, that our conclusions on and interpretations of
the record are really and strictly only valid so long as we confine
ourselves to one vertical section. I do not mean to tell you that there
are no qualifying circumstances, so that, even in very considerable
areas, we may safely speak of conformably superimposed beds being older
or younger than others at many different points. But we can never be
quite sure in coming to that conclusion, and especially we cannot
be sure if there is any break in their continuity, or any very great
distance between the points to be compared.
Well now, so much for the record itself,--so much for its
imperfections,--so much for the conditions to be observed in
interpreting it, and its chronological indications, the moment we pass
beyond the limits of a vertical linear section.
Now let us pass from the record to that which it contains,--from the
book itself to the writing and the figures on its pages. This writing
and these figures consist of remains of animals and plants which, in the
great majority of cases, have lived and died in the very spot in which
we now find them, or at least in the immediate vicinity. You must all of
you be aware--and I referred to the fact in my last lecture--that there
are vast numbers of creatures living at the bottom of the sea. These
creatures, like all others, sooner or later die, and their shells and
hard parts lie at the bottom; and then the fine mud which is being
constantly brought down by rivers and the action of the wear and tear of
the sea, covers them over and protects them from any further change
or alteration; and, of course, as in process of time the mud becomes
hardened and solidified, the shells of these animals are preserved
and firmly imbedded in the limestone or sandstone which is being thus
formed. You may see in the galleries of the Museum up stairs specimens
of limestones in which such fossil remains of existing animals are
imbedded. There are some specimens in which turtles' eggs have been
imbedded in calcareous sand, and before the sun had hatched the young
turtles, they became covered over with calcareous mud, and thus have
been preserved and fossilized.
Not only does this process of imbedding and fossilization occur with
marine and other aquatic animals and plants, but it affects those land
animals and plants which are drifted away to sea, or become buried in
bogs or morasses; and the animals which have been trodden down by their
fellows and crushed in the mud at the river's bank, as the herd have
come to drink. In any of these cases, the organisms may be crushed or be
mutilated, before or after putrefaction, in such a manner that perhaps
only a part will be left in the form in which it reaches us. It is,
indeed, a most remarkable fact, that it is quite an exceptional case
to find a skeleton of any one of all the thousands of wild land animals
that we know are constantly being killed, or dying in the course of
nature: they are preyed on and devoured by other animals or die in
places where their bodies are not afterwards protected by mud. There are
other animals existing in the sea, the shells of which form exceedingly
large deposits. You are probably aware that before the attempt was made
to lay the Atlantic telegraphic cable, the Government employed vessels
in making a series of very careful observations and soundings of the
bottom of the Atlantic; and although, as we must all regret, up to the
present time that project has not succeeded, we have the satisfaction
of knowing that it yielded some most remarkable results to science.
The Atlantic Ocean had to be sounded right across, to depths of several
miles in some places, and the nature of its bottom was carefully
ascertained. Well, now, a space of about 1,000 miles wide from east to
west, and I do not exactly know how many from north to south, but at
any rate 600 or 700 miles, was carefully examined, and it was found that
over the whole of that immense area an excessively fine chalky mud is
being deposited; and this deposit is entirely made up of animals whose
hard parts are deposited in this part of the ocean, and are doubtless
gradually acquiring solidity and becoming metamorphosed into a chalky
limestone. Thus, you see, it is quite possible in this way to preserve
unmistakable records of animal and vegetable life. Whenever the
sea-bottom, by some of those undulations of the earth's crust that I
have referred to, becomes upheaved, and sections or borings are made,
or pits are dug, then we become able to examine the contents and
constituents of these ancient sea-bottoms, and find out what manner of
animals lived at that period.
Now it is a very important consideration in its bearing on the
completeness of the record, to inquire how far the remains contained
in these fossiliferous limestones are able to convey anything like an
accurate or complete account of the animals which were in existence
at the time of its formation. Upon that point we can form a very clear
judgment, and one in which there is no possible room for any mistake.
There are of course a great number of animals--such as jelly-fishes,
and other animals--without any hard parts, of which we cannot reasonably
expect to find any traces whatever: there is nothing of them to
preserve. Within a very short time, you will have noticed, after they
are removed from the water, they dry up to a mere nothing; certainly
they are not of a nature to leave any very visible traces of their
existence on such bodies as chalk or mud. Then again, look at land
animals; it is, as I have said, a very uncommon thing to find a land
animal entire after death. Insects and other carnivorous animals very
speedily pull them to pieces, putrefaction takes place, and so, out of
the hundreds of thousands that are known to die every year, it is the
rarest thing in the world to see one imbedded in such a way that its
remains would be preserved for a lengthened period. Not only is this the
case, but even when animal remains have been safely imbedded, certain
natural agents may wholly destroy and remove them.
Almost all the hard parts of animals--the bones and so on--are composed
chiefly of phosphate of lime and carbonate of lime. Some years ago, I
had to make an inquiry into the nature of some very curious fossils
sent to me from the North of Scotland. Fossils are usually hard bony
structures that have become imbedded in the way I have described, and
have gradually acquired the nature and solidity of the body with which
they are associated; but in this case I had a series of 'holes' in some
pieces of rock, and nothing else. Those holes, however, had a certain
definite shape about them, and when I got a skilful workman to make
castings of the interior of these holes, I found that they were the
impressions of the joints of a backbone and of the armour of a great
reptile, twelve or more feet long. This great beast had died and got
buried in the sand; the sand had gradually hardened over the bones, but
remained porous. Water had trickled through it, and that water being
probably charged with a superfluity of carbonic acid, had dissolved all
the phosphate and carbonate of lime, and the bones themselves had thus
decayed and entirely disappeared; but as the sandstone happened to have
consolidated by that time, the precise shape of the bones was retained.
If that sandstone had remained soft a little longer, we should have
known nothing whatsoever of the existence of the reptile whose bones it
had encased.
How certain it is that a vast number of animals which have existed
at one period on this earth have entirely perished, and left no trace
whatever of their forms, may be proved to you by other considerations.
There are large tracts of sandstone in various parts of the world, in
which nobody has yet found anything but footsteps. Not a bone of any
description, but an enormous number of traces of footsteps. There is no
question about them. There is a whole valley in Connecticut covered with
these footsteps, and not a single fragment of the animals which made
them has yet been found. Let me mention another case while upon that
matter, which is even more surprising than those to which I have yet
referred. There is a limestone formation near Oxford, at a place called
Stonesfield, which has yielded the remains of certain very interesting
mammalian animals, and up to this time, if I recollect rightly, there
have been found seven specimens of its lower jaws, and not a bit of
anything else, neither limb-bones nor skull, or any part whatever; not
a fragment of the whole system! Of course, it would be preposterous
to imagine that the beasts had nothing else but a lower jaw!
The probability is, as Dr. Buckland showed, as the result of his
observations on dead dogs in the river Thames, that the lower jaw, not
being secured by very firm ligaments to the bones of the head, and being
a weighty affair, would easily be knocked off, or might drop away from
the body as it floated in water in a state of decomposition. The jaw
would thus be deposited immediately, while the rest of the body would
float and drift away altogether, ultimately reaching the sea, and
perhaps becoming destroyed. The jaw becomes covered up and preserved
in the river silt, and thus it comes that we have such a curious
circumstance as that of the lower jaws in the Stonesfield slates. So
that, you see, faulty as these layers of stone in the earth's crust
are, defective as they necessarily are as a record, the account of
contemporaneous vital phenomena presented by them is, by the necessity
of the case, infinitely more defective and fragmentary.
It was necessary that I should put all this very strongly before you,
because, otherwise, you might have been led to think differently of the
completeness of our knowledge by the next facts I shall state to you.
The researches of the last three-quarters of a century have, in truth,
revealed a wonderful richness of organic life in those rocks. Certainly
not fewer than thirty or forty thousand different species of fossils
have been discovered. You have no more ground for doubting that these
creatures really lived and died at or near the places in which we find
them than you have for like scepticism about a shell on the sea-shore.
The evidence is as good in the one case as in the other.
Our next business is to look at the general character of these fossil
remains, and it is a subject which it will be requisite to consider
carefully; and the first point for us is to examine how much the
extinct 'Flora' and 'Fauna' as a 'whole'--disregarding altogether
the 'succession' of their constituents, of which I shall speak
afterwards--differ from the 'Flora' and 'Fauna' of the present day;--how
far they differ in what we 'do' know about them, leaving altogether out
of consideration speculations based upon what we 'do not' know.
I strongly imagine that if it were not for the peculiar appearance that
fossilised animals have, any of you might readily walk through a museum
which contains fossil remains mixed up with those of the present forms
of life, and I doubt very much whether your uninstructed eyes would
lead you to see any vast or wonderful difference between the two. If
you looked closely, you would notice, in the first place, a great many
things very like animals with which you are acquainted now: you would
see differences of shape and proportion, but on the whole a close
similarity.
I explained what I meant by ORDERS the other day, when I described the
animal kingdom as being divided in sub-kingdoms, classes and orders. If
you divide the animal kingdom into orders, you will find that there are
about one hundred and twenty. The number may vary on one side or the
other, but this is a fair estimate. That is the sum total of the orders
of all the animals which we know now, and which have been known in past
times, and left remains behind.
Now, how many of those are absolutely extinct? That is to say, how many
of these orders of animals have lived at a former period of the world's
history, but have at present no representatives? That is the sense in
which I meant to use the word "extinct." I mean that those animals did
live on this earth at one time, but have left no one of their kind
with us at the present moment. So that estimating the number of extinct
animals is a sort of way of comparing the past creation as a whole with
the present as a whole. Among the mammalia and birds there are none
extinct; but when we come to the reptiles there is a most wonderful
thing: out of the eight orders, or thereabouts, which you can make among
reptiles, one-half are extinct. These diagrams of the plesiosaurus,
the ichthyosaurus, the pterodactyle, give you a notion of some of these
extinct reptiles. And here is a cast of the pterodactyle and bones of
the ichthyosaurus and the plesiosaurus, just as fresh as if it had been
recently dug up in a churchyard. Thus, in the reptile class, there are
no less than half of the orders which are absolutely extinct. If we turn
to the 'Amphibia', there was one extinct order, the Labyrinthodonts,
typified by the large salamander-like beast shown in this diagram.
No order of fishes is known to be extinct. Every fish that we find in
the strata--to which I have been referring--can be identified and placed
in one of the orders which exist at the present day. There is not known
to be a single ordinal form of insect extinct. There are only two orders
extinct among the 'Crustacea'. There is not known to be an extinct order
of these creatures, the parasitic and other worms; but there are
two, not to say three, absolutely extinct orders of this class, the
'Echinodermata'; out of all the orders of the 'Coelenterata' and
'Protozoa' only one, the Rugose Corals.
So that, you see, out of somewhere about 120 orders of animals, taking
them altogether, you will not, at the outside estimate, find above ten
or a dozen extinct. Summing up all the orders of animals which have left
remains behind them, you will not find above ten or a dozen which cannot
be arranged with those of the present day; that is to say, that the
difference does not amount to much more than ten per cent.: and the
proportion of extinct orders of plants is still smaller. I think that
that is a very astounding, a most astonishing fact, seeing the enormous
epochs of time which have elapsed during the constitution of the surface
of the earth as it at present exists; it is, indeed, a most astounding
thing that the proportion of extinct ordinal types should be so
exceedingly small.
But now, there is another point of view in which we must look at this
past creation. Suppose that we were to sink a vertical pit through the
floor beneath us, and that I could succeed in making a section right
through in the direction of New Zealand, I should find in each of the
different beds through which I passed the remains of animals which I
should find in that stratum and not in the others. First, I should come
upon beds of gravel or drift containing the bones of large animals, such
as the elephant, rhinoceros, and cave tiger. Rather curious things to
fall across in Piccadilly! If I should dig lower still, I should come
upon a bed of what we call the London clay, and in this, as you will see
in our galleries upstairs, are found remains of strange cattle, remains
of turtles, palms, and large tropical fruits; with shell-fish such as
you see the like of now only in tropical regions. If I went below
that, I should come upon the chalk, and there I should find something
altogether different, the remains of ichthyosauri and pterodactyles, and
ammonites, and so forth.
I do not know what Mr. Godwin Austin would say comes next, but probably
rocks containing more ammonites, and more ichthyosauri and plesiosauri,
with a vast number of other things; and under that I should meet with
yet older rocks, containing numbers of strange shells and fishes; and in
thus passing from the surface to the lowest depths of the earth's crust,
the forms of animal life and vegetable life which I should meet with
in the successive beds would, looking at them broadly, be the more
different the further that I went down. Or, in other words, inasmuch
as we started with the clear principle, that in a series of
naturally-disposed mud beds the lowest are the oldest, we should come
to this result, that the further we go back in time the more difference
exists between the animal and vegetable life of an epoch and that which
now exists. That was the conclusion to which I wished to bring you at
the end of this Lecture.
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