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may be obtained in prodigious niunbers by the use of a prop- 30
erly constructed net. Hence it follows that these silicious
organisms, though they are not heavier than the lightest dust,
must have fallen, in some cases, through fifteen thousand feet
of water, before they reached their final resting-place on the
ocean floor. And considering how large a surface these bodies 35
expose in proportion to their weight, it is probable that they
occupy a great length of time in making their burial journey
from the surface of the Atlantic to the bottom.



ON" A PIECE OF CHALK 309

But if the Badiolarice and Diatoms are thus rained upon the
bottom of the sea, from the superficial hiyer of its waters in
which they pass their lives, it is obviously possible that the
Glohiger'mce may be similarly derived; and if they were so,
5 it would be much more easy to understand how tliey obtain
their supply of food than it is at present. Nevertheless the
positive and negative evidence all points the other way. The
skeletons of the full-grown, deep-sea Glohigerince are so
remarkably solid and heavy in proportion to their surface as

10 to seem little fitted for floating ; and as a matter of fact they
are not to be found along with the Diatoms and Badiolarice in
the uppermost stratum of the open ocean. It has been ob-
served, again, that the abundance of Glohigerince, in propor-
tion to other organisms of like kind, increases with the depth of

15 the sea, and that deep-water Glohigerince are larger than those
which live in shallower parts of the sea ; and such facts nega-
tive the supposition that these organisms have been swept by
currents from the shallows into the deeps of the Atlantic. It
therefore seems to be hardly douljtful that these wonderful

30 creatures live and die at the depths in which they are found.

However, the important points for us are that the living

Glohigerince are exclusively marine animals, the skeletons of

which abound at the bottom of deep seas, and that there

is not a shadow of reason for believing that the habits of the

25 Glohigerince of the chalk differed from those of the existing
species. But if this be true, there is no escaping the conclusion
that the chalk itself is the dried mud of an ancient deep sea.

In working over the soundings collected by Captain
Dayman, I was surprised to find that many of what I have

30 called the •' granules " of that mud were not, as one might
have been tempted to think at first, the mere powder and waste
of Glohigerince, but that they had a definite form and size.
I termed these bodies " coccoliths," and doubted their organic
nature. Dr. Wallich verified my observation, and added the

35 interesting discovery that not unfrequently bodies similar to
these coccoliths were aggregated together into spheroids, which
he termed " coccospheres." So far as we knew, these bodies,
the nature of which is extremely puzzling and problematical,



310 THOMAS HE^RY HUXLEY

were peculiar to the Atlantic soundings. But a few years ago
Mr. Sorby. in making a careful examination of the chalk by
means of thin sections and otherwise, observed, as Ehrenberg
had done before him, that much of its granular basis possesses
a definite form. Comparing these formed particles with 5
those in the Atlantic soundings, he found the two to be
identical, and thus proved that the chalk, like the sound-
ings, contains these mysterious coccoliths and coccospheres.
Here was a further and a most interesting confirmation, from
internal evidence, uf the essential identity of the chalk with 10
modern deep-sea mud. Glohigerina', coccoliths, and coc-
cospheres are found as the chief constituents of both and tes-
tify to the general similarity of the conditions under which
both have been formed.

The evidence furnished by the hewing, facing, and super- 15
position of the stones of the Pyramids that these structures
were built by men has no greater weight than the evidence
that the chalk was built by GJohigerince; and the belief that
those ancient pyramid-builders were terrestrial and air-
breathing creatures like ourselves is not better based than the 30
conviction that the chalk-makers lived in the sea. But as our
belief in the building of the Pyramids by men is not only
grounded on the internal evidence afforded by these structures,
but gathers strength from multitudinous collateral proofs and
is clinched by the total absence of any reason for a contrary 25
belief, so the evidence drawn from the Glohigerina' that the
chalk is an ancient sea-bottom is fortified by innumerable
independent lines of evidence; and our belief in the truth of
the conclusion to which all positive testimony tends receives
the like negative justification from the fact that no other 30
hypothesis has a shadow of foundation.

H may be worth while briefly to consider a few of these
collateral proofs that the chalk was deposited at the bottom
of the sea. The great mass of the chalk is composed, as we
have seen, of the skeletons of Glohigerince and other simple 35
organisms, imbedded in granular matter. Here and there,
however, this hardened mud of the ancient sea reveals the
remains of higher animals which have lived and died and left



ON A PIECE OF CHALK 311

their hard parts in the nuid, just as the oysters die and leave
their shells behind them in the mud of the present seas.

There are certain groups of animals at the present day
which are never found in fresh waters, being unable to live

5 anywhere but in the sea. Such are the corals ; those corallines
which are called Polyzoa; those creatures which fabricate the
lampshells, and are called Bradiiopoda; the pearly Nautilus,
and all animals allied to it; and all the forms of sea-urchins
and star-fishes. Not only are all these creatures confined to

10 salt water at the present day, but, so far as our records of the
past go, the conditions of their existence have been the same;
hence their occurrence in any deposit is as strong evidence as
can be obtained that that deposit was formed in the sea.
Now, the remains of animals of all the kinds which have been

15 enumerated occur in the chalk, in greater or less abundance,
while not one of those forms of shell-fish which are character-
istic of fresh water has yet been observed in it.

When we consider that the remains of inore than three
thousand distinct species of aquatic animals have been dis-

20 covered among the fossils of the chalk, that the great majority
of them are of such forms as are now met with only in the
sea, and that there is no reason to believe that any one of them
inhabited fresh water, the collateral evidence that the chalk
represents an ancient sea-bottom acquires as great force as

25 the proof derived from the nature of the chalk itself. I think
you will now allow that I did not overstate my case when I
asserted that we have as strong grounds for believing that all
the vast area of dry land at present occupied by the chalk
was once at the bottom of the sea as we have for any matter of

30 history whatever; while there is no justification for any other
belief.

No less certain is it that the time during which the countries
we now call southeast Enghind, France, Germany, Poland.
Russia, Egypt, Arabia, Syria were more or less completely

35 covered by a deep sea was of considerable duration. We have
already seen that the chalk is in places more than a thousand
feet thick. I think you will agree with me that it must have
taken some time for the skeletons of aninmlculte of an hun-



312 THOMAS HENEY HUXLEY

dredth of an inch in diameter to lieap up such a mass as that.
I have said that throughout the thickness of the chalk the re-
mains of other animals are scattered. These remains are often
in the most exquisite state of preservation. The valves of the
shell-fishes are commonly adherent ; the long spines of some 5
of the sea-urchins, which would be detached by the smallest
jar, often remain in their places. In a word, it is certain
that these animals have lived and died when the place which
they now occupy was the surface of as much of the chalk as
had then been deposited, and that each has been covered up 10
by the layer of GJohigerina mud, upon which the creatures
imbedded a little higher up have in like manner lived and
died. But some of these remains prove the existence of rep-
tiles of vast size in the chalk sea. These lived their time, and
had their ancestors and descendants, which assuredly implies 15
time, reptiles being of slow growth.

There is more curious evidence, again, that the process of
covering up, or in other words the deposit of Glohigerina
skeletons, did not go on very fast. It is demonstrable that
an animal of the cretaceous sea might die, that its skeleton 20
might lie uncovered upon the sea-bottom long enough to lose
all its outward coverings and appendages by putrefaction ;
and that, after this had happened, another animal might
attach itself to the dead and naked skeleton, might grow to
maturity, and might itself die before the calcareous mud had 35
buried the whole.

Cases of this kind are admirably described by Sir Charles
Lyell. He speaks of the frequency with which geologists
find in the chalk a fossilized sea-urchin, to which is attached
the lower valve of a Crania. This is a kind of shell-fish, 30
with a shell composed of two pieces, of which, as in the oyster,
one is fixed and the other free. " The upper valve is almost
invariably wanting, though occasionally found in a perfect
state of preservation in the white chalk at some distance. In
this case we see clearly that the sea-urchin first lived from 35
youth to age, then died and lost its spines, which were carried
away. Then the young Crania adhered to the bared shell,
grew and perished in its turn; after which the upper valve



ON A PIECE OF CHALK BIB

was separated from the lower ))efore the Echinus hecame
enveloped in chalky mud."

A specimen in the Museum of Practical Geolog}', in Lon-
don, still further prolongs the period which must have elapsed
5 between the death of the sea-urchin and its burial by the
Glohigerince. For the outward face of the valve of a Crania,
which is attached to a sea-urchin (Micnisfpr), is itself over-
run by an incrusting coralline, which spreads thence over
more or less of the surface of the sea-urchin. It follows that.

10 after the upper valve of the Crania fell off, the surface of the
attached valve must have remained exposed long enough to
allow of the growth of the whole coralline, since corallines
do not live imbedded in mud.

The progress of knowledge may one day enable us to deduce

15 from such facts as these the maximum rate at which the chalk
can have accumulated, and thus to arrive at the minimum du-
ration of the chalk period. Suppose that the valve of the
Crania upon which a coralline has fixed itself, in the way just
described, is so attached to the sea-urchin that no part of it is

20 more than an inch above the face upon which the sea-urchin
rests. Then, as the coralline could not have fixed itself if
the Crania had been covered up with chalk mud, and could
not have lived had itself been so covered, it follows that an
inch of chalk mud could not have accumulated within the

25 time between the death and decay of the soft parts of the
sea-urchin and the growth of the. coralline to the full size
which it has attained. If the decay of the soft parts of the
sea-urchin, the attachment, growth to maturity, and decay of
the Crania, and the subsequent attachment and growth of the

30 coralline took a year (which is a low estimate enough), fhe
accumulation of the inch of chalk must have taken more than
a year ; and the deposit of a thousand feet of chalk must conse-
quently have taken more than twelve thousand years. The
foundation of all this calculation is of course a knowledge of

35 the length of time the Crania and the coralline needed to at-
tain their full size; and on this head precise knowledge is at
present wanting. But there are circumstances which tend to
show that nothing like an inch of chalk has accumulated



314 THOMAS HENRY HUXLEY

during the life of a Crania; and on any probable estimate of
the length of that life the clialk ])L'riod must have had a much
longer duration than that thus roughly assigned to it.

Thus not only is it certain that the chalk is the mud of an
ancient sea-bottom, but it is no less certain that the chalk sea 5
existed during an extremely long period, though we may not
be prepared to give a precise estimate of the length of that
period in years. The relative duration is clear, though the
absolute duration may not be definable. The attempt to affix
any precise date to the period at which the chalk sea began or lo
ended its existence is baffled by difficulties of the same kind.
But the relative age of the cretaceous epoch may be determined
with as great ease and certainty as the long duration of that
epoch.

You will have heard of the interesting discoveries, recently 15
made in various parts of Western Europe, of flint implements
obviously worked into shape by -human hands, under circum-
stances which show conclusively that man is a very ancient
denizen of these regions. It has been proved that the old
populations of Europe whose existence has been revealed to us 20
in this way, consisted of savages, such as the Esquimaux are
now; that in the country which is now France they hunted the
reindeer, and were familiar with the ways of the mammoth
and the bison. The physical geography of France was in those
days different from what it is now — the river Somme. for 25
instance, having cut its bed a hundred feet deeper between
that time and this ; and it is probable that the climate was more
like that of Canada or Siberia than that of Western Europe.

The existence of these people is forgotten even in the tradi-
tions of the oldest historical nations. The name and fame of 30
them had utterly vanished until a few years back ; and the
amount of physical change which has been effected since their
day renders it more than probable that, venerable as are some
of the historical nations, the workers of the chipped flints
of Hoxne or of Amiens are to them as they are to us in point 35
of antiquity. But il we assign to these hoar relics of long
vanished generations of men the greatest age that can possibly
be claimed for them, they are not older than the drift, or



ON A PIECE OF CHALK 315

boulder clay, which in comparison with the chalk is but a very
juvenile deposit. You need go no further than your own sea-
board for evidence of this fact. At one of the most charming
spots on the coast of Norfolk, Cromer, you will see the boulder

5 clay forming a vast mass, which lies upon the chalk and must
consequently have come into existence after it. Huge boulders
of chaLk are in fact included in the clay, and have evidently
been brought to the position they now occupy l)y the same
agency as that which has planted blocks of syenite from Nor-

10 way side by side with them.

The chalk, then, is certainly older than the boulder clay. If
you ask how much, I will again take you no further than the
same spot upon your own coasts for evidence. I have spoken
of the boulder clay and drift as resting upon the chalk. That

15 is not strictly true. Interposed between the chalk and the
drift is a comparatively insignificant layer, containing vege-
table matter. But that layer tells a wonderful history. It is
full of stumps of trees standing as they grew. Fir-trees are
there with their cones, and hazel -bushes with their nuts ; there

20 stand the stools of oak and yew trees, beeches and alders.
Hence this stratum is appropriately called the " forest-bed."

It is obvious that the chalk must have been upheaved and
converted into dry land before the timber trees could grow
upon it. As the boles of some of these trees are from two to

25 three feet in diameter, it is no less clear that the dry land thus
formed remained in the same conditions for long ages. And
not only do the remains of stately oaks and well-grown firs
testify to the duration of this condition of things, but addi-
tional evidence to the same effect is afforded by the abundant

30 remains of elephants, rhinoceroses, hippopotamuses, and other
great wild beasts, which it has yielded to the zealous search of
such men as the Eev. Mr. Gunn. ^Y\\en you look at such a
cellection as he has formed, and bethink you that these ele-
phantine bones did verital)ly carry their owners about, and

35 these great grinders crunch, in the dark woods of which the
forest-bed is now the only trace, it is impossible not to feel
that they are as good evidence of the lapse of time as the
annual rings of the tree stumps.



316 THOMAS HENRY HUXLEY

Thus tliere is a writing upon the wall of cliffs at Cromer,
and whoso runs may read it. It tells us, with an authority
A\hieh cannot be impeached, that the ancient sea-bed of the
chalk-sea was raised up, and remained dry land until it was
covered with forest stocked with the great game, the spoils 5
of which have rejoiced your geologists. How long it re-
mained in that condition cannot be said ; l)ut " the whirligig
of time brought its revenges " in those days as in these.
That dry land, with the bones and teeth of generations of
long-lived elephants, hidden away among the gnarled roots 10
and dried leaves of its ancient trees, sank gradually to the
bottom of the icy sea, which covered it with huge masses of
drift and boulder clay. Sea-beasts, such as the walrus, now
restricted to the extreme north, paddled about where birds
had twittered among the topmost twigs of the fir-trees. How 15
long this state of things endured we know not, but at length
it came to an end. The upheaved glacial mud hardened into
the soil of modern Norfolk. Forests grew once more, the
wolf and the beaver replaced the reindeer and the elephant;
and at length what we call the history of England dawned. 20

Thus you have, within the limits of your own county, proof
that the chalk can justly claim a very much greater antiquity
than even the oldest physical traces of mankind. But we
may go further and demonstrate, by evidence of the same
authority as that which testifies to the existence of the father 25
of men, that the chalk is vastly older than Adam himself.
The Bool' of Genesis informs us that Adam, immediately
upon his creation and before the appearance of Eve, was
placed in the Garden of Eden. The problem of the geo-
graphical position of Eden has greatly vexed the spirits of the 30
learned in such matters; but there is one point respecting
A\hich, so far as I know, no commentator has ever raised a
doubt. This is that of the four rivers which are said to run
out of it Euphrates and Hiddekel are identical with the
rivers now known by the names of Euphrates and Tigris. 35
But the whole country in which these mighty rivers take
their origin, and through which they run, is composed of
rocks which are either of the same age as the chalk or of later



01^ A PIECE OF CHALK 317

date. So that the chalk must not only have been formed, but
after its formation the time required for the deposit of these
later rocks and for their upheaval into dry land must have
elapsed, before the smallest brook which feeds the swift stream
5 of " the great river, the river of Babylon," began to flow.

Thus evidence which cannot be rebutted and which need
not be strengthened, though if time permitted I might in-
definitely increase its quantity, compels you to believe that the
earth, from the time of the chalk to the present day, has been

10 the theatre of a series of changes as vast in their amount as
they were slow in their progress. The area on which we
staiid has been first sea and then land, for at least four alter-
nations, and has remained in each of these conditions for a
period of great length. Nor have these wonderful metamor-

15 phoses of sea into land and of land into sea been confined to
one corner of England. During the chalk period, or " creta-
ceous epoch," not one of the present great physical features
of the globe was in existence. Our great mountain ranges,
Pyrenees, Alps, Himalayas, Andes, have all been upheaved

20 since the chalk was deposited and the cretaceous sea flowed
over the sites of Sinai and Ararat. All this is certain, be-
cause rocks of cretaceous or still later date have shared in
the elevatory movements which gave rise to these mountain
chains, and may be found perched up, in some cases, many

25 thousand feet high upon their flanks. And evidence of equal
cogency demonstrates that, though in Norfolk the forest-bed
rests directly upon the chalk, yet it does so, not because the
period at which the forest grew immediately followed that at
which the chalk was formed, but because an immense lapse

30 of time, represented elsewhere by thousands of feet of rock,
is not indicated at Cromer.

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

35 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
Avhich were formed in still older oceans,



318 TH0MA8 HEXRY HUXLEY

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 inhal)itants. All the
great classes of animals, beasts of the field, fowls of the air.
creeping things, and things which dwell in the waters, flour- 5
ished upon the globe long ages before the chalk was deposited.
Yerj 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 10
before the chalk, were not our beasts of the field, nor the
fowls of the air such as those which the eye of man has seen
flying, unless his antiquity dates inflnitely 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 15
before it was colonized. "We should see mammals, birds, rep-
tiles, fishes, insects, snails, and the like, clearly recognizable
as such, and yet not one of them would be just the same as
those with which we are familiar, and many would be ex-
tremely different. 20

From that time to the present the population of the world
has undergone slow and gradual but incessant changes.
There has been no grand catastrophe — no 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 an- 25
other has taken its place ; creatures of one type of structure
have dimin'shed, 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 pres-
ent day. appear startling if placed side by side, we are led 30
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 con- 35
nected. The groups which are dying out flourish side by side
Avith the groups which are now the dominant forms of life.
Thus the chalk contains remains of those strange flying and



0^ A PIECE OF CHALK 319

swimming reptiles, the pterodactyl, the irJithyosaurus, and
the phsiosaunis, 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
5 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

10 similar to existing species, almost supplant the forms of fish
which predominate in more ancient seas ; and many kinds of
living shell-fish first became 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

15 existed at that remote epoch. The Ghbigerina of the present
day, for example, is not different specifically from that of
the chalk; and the same may be said of many other Fora-



Online LibraryWalter Cochrane BronsonEnglish essays → online text (page 28 of 37)