Discourses - Thomas H. Huxley
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The result of all these operations is, that we know the contours and the
nature of the surface-soil covered by the North Atlantic for a distance
of 1,700 miles from east to west, as well as we know that of any part of
the dry land. It is a prodigious plain--one of the widest and most even
plains in the world. If the sea were drained off, you might drive a
waggon all the way from Valentia, on the west coast of Ireland, to
Trinity Bay, in Newfoundland. And, except upon one sharp incline about
200 miles from Valentia, I am not quite sure that it would even be
necessary to put the skid on, so gentle are the ascents and descents upon
that long route. From Valentia the road would lie down-hill for about 200
miles to the point at which the bottom is now covered by 1,700 fathoms of
sea-water. Then would come the central plain, more than a thousand miles
wide, the inequalities of the surface of which would be hardly
perceptible, though the depth of water upon it now varies from 10,000 to
15,000 feet; and there are places in which Mont Blanc might be sunk
without showing its peak above water. Beyond this, the ascent on the
American side commences, and gradually leads, for about 300 miles, to the
Newfoundland shore.
Almost the whole of the bottom of this central plain (which extends for
many hundred miles in a north and south direction) is covered by a fine
mud, which, when brought to the surface, dries into a greyish white
friable substance. You can write with this on a blackboard, if you are so
inclined; and, to the eye, it is quite like very soft, grayish chalk.
Examined chemically, it proves to be composed almost wholly of carbonate
of lime; and if you make a section of it, in the same way as that of the
piece of chalk was made, and view it with the microscope, it presents
innumerable _Globigerinoe_ embedded in a granular matrix. Thus this deep-
sea mud is substantially chalk. I say substantially, because there are a
good many minor differences; but as these have no bearing on the question
immediately before us,--which is the nature of the _Globigerinoe_ of the
chalk,--it is unnecessary to speak of them.
_Globigerinoe_ of every size, from the smallest to the largest, are
associated together in the Atlantic mud, and the chambers of many are
filled by a soft animal matter. This soft substance is, in fact, the
remains of the creature to which the _Globigerinoe_ shell, or rather
skeleton, owes its existence--and which is an animal of the simplest
imaginable description. It is, in fact, a mere particle of living jelly,
without defined parts of any kind--without a mouth, nerves, muscles, or
distinct organs, and only manifesting its vitality to ordinary
observation by thrusting out and retracting from all parts of its
surface, long filamentous processes, which serve for arms and legs. Yet
this amorphous particle, devoid of everything which, in the higher
animals, we call organs, is capable of feeding, growing, and multiplying;
of separating from the ocean the small proportion of carbonate of lime
which is dissolved in sea-water; and of building up that substance into a
skeleton for itself, according to a pattern which can be imitated by no
other known agency.
The notion that animals can live and flourish in the sea, at the vast
depths from which apparently living _Globigerinoe_; have been brought up,
does not agree very well with our usual conceptions respecting the
conditions of animal life; and it is not so absolutely impossible as it
might at first sight appear to be, that the _Globigcrinoe_ of the
Atlantic sea-bottom do not live and die where they are found.
As I have mentioned, the soundings from the great Atlantic plain are
almost entirely made up of _Globigerinoe_, with the granules which have
been mentioned, and some few other calcareous shells; but a small
percentage of the chalky mud--perhaps at most some five per cent. of it--
is of a different nature, and consists of shells and skeletons composed
of silex, or pure flint. These silicious bodies belong partly to the
lowly vegetable organisms which are called _Diatomaceoe_, and partly to
the minute, and extremely simple, animals, termed _Radiolaria_. It is
quite certain that these creatures do not live at the bottom of the
ocean, but at its surface--where they may be obtained in prodigious
numbers by the use of a properly 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 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.
But if the _Radiolaria_ and Diatoms are thus rained upon the bottom of
the sea, from the superficial layer of its waters in which they pass
their lives, it is obviously possible that the _Globigerinoe_ may be
similarly derived; and if they were so, it would be much more easy to
understand how they 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 _Globigerinoe_ are so
remarkably solid and heavy in proportion to their surface as to seem
little fitted for floating; and, as a matter of fact, they are not to be
found along with the Diatoms and _Radiolaria_ in the uppermost stratum of
the open ocean. It has been observed, again, that the abundance of
_Globigerinoe_, in proportion to other organisms, of like kind, increases
with the depth of the sea; and that deep-water _Globigerinoe_ are larger
than those which live in shallower parts of the sea; and such facts
negative 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 doubtful that these wonderful creatures live and die at the
depths in which they are found.[2]
[Footnote 2: During the cruise of H.M.S. _Bulldog_, commanded by Sir
Leopold M'Clintock, in 1860, living star-fish were brought up, clinging
to the lowest part of the sounding-line, from a depth of 1,260 fathoms,
midway between Cape Farewell, in Greenland, and the Rockall banks. Dr.
Wallich ascertained that the sea-bottom at this point consisted of the
ordinary _Globigerina_ ooze, and that the stomachs of the star-fishes
were full of _Globigerinoe_. This discovery removes all objections to the
existence of living _Globigerinoe_ at great depths, which are based upon
the supposed difficulty of maintaining animal life under such conditions;
and it throws the burden of proof upon those who object to the
supposition that the _Globigerinoe_ live and die where they are found.]
However, the important points for us are, that the living _Globigerinoe_
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 _Globigerinoe_ 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 called the "granules" of that
mud were not, as one might have been tempted to think at first, the more
powder and waste of _Globigerinoe_, 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 interesting
discovery that, not unfrequently, bodies similar to these "coccoliths"
were aggregated together into spheroids, which lie termed
"_coccospheres_." So far as we knew, these bodies, the nature of which is
extremely puzzling and problematical, 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
those in the Atlantic soundings, he found the two to be identical; and
thus proved that the chalk, like the surroundings, contains these
mysterious coccoliths and coccospheres. Here was a further and most
interesting confirmation, from internal evidence, of the essential
identity of the chalk with modern deep-sea mud. _Globigerinoe_,
coccoliths, and coccospheres are found as the chief constituents of both,
and testify to the general similarity of the conditions under which both
have been formed.[3]
[Footnote 3: I have recently traced out the development of the
"coccoliths" from a diameter of 1/7000th of an inch up to their largest
size (which is about 1/1000th), and no longer doubt that they are
produced by independent organisms, which, like the _Globigerinoe_, live
and die at the bottom of the sea.]
The evidence furnished by the hewing, facing, and superposition 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
_Globigerinoe_; and the belief that those ancient pyramid-builders were
terrestrial and air-breathing creatures like ourselves, is not better
based than the 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 belief; so the evidence drawn from
the _Globigerinoe_ 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 hypothesis has a
shadow of foundation.
It 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
_Globigerinoe_, and other simple 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 their hard
parts in the mud, just as the oysters die and leave their shells behind
them, in the mud of the present seas.
There are, at the present day, certain groups of animals which are never
found in fresh waters, being unable to live anywhere but in the sea. Such
are the corals; those corallines which are called _Polyzoa_; those
creatures which fabricate the lamp-shells, and are called _Brachiopoda_;
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
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 enumerated, occur in the chalk, in greater or less
abundance; while not one of those forms of shell-fish which are
characteristic of fresh water has yet been observed in it.
When we consider that the remains of more than three thousand distinct
species of aquatic animals have been discovered 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 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 history whatever; while there is no justification for any
other belief.
No less certain it is that the time during which the countries we now
call south-east England, France, Germany, Poland, Russia, Egypt, Arabia,
Syria, were more or less completely 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 animalcules of a hundredth
of an inch in diameter to heap up such a mass as that. I have said that
throughout the thickness of the chalk the remains 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 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 by the layer of _Globigerina_ 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 reptiles
of vast size in the chalk sea. These lived their time, and had their
ancestors and descendants, which assuredly implies 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 _Globigerina_ skeletons, did not go on
very fast. It is demonstrable that an animal of the cretaceous sea might
die, that its skeleton 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 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, 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 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 was separated from the lower, before the
Echinus became enveloped in chalky mud."[4]
A specimen in the Museum of Practical Geology, in London, still further
prolongs the period which must have elapsed between the death of the sea-
urchin, and its burial by the _Globigerinoe_. For the outward face of the
valve of a _Crania_, which is attached to a sea-urchin, (_Micraster_), is
itself overrun by an incrusting coralline, which spreads thence over more
or less of the surface of the sea-urchin. It follows that, 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 embedded in mud.[4]
[Footnote 4: _Elements of Geology_, by Sir Charles Lyell, Bart. F.B.S.,
p. 23.]
The progress of knowledge may, one day, enable us to deduce from such
facts as these the maximum rate at which the chalk can have accumulated,
and thus to arrive at the minimum duration of the chalk period. Suppose
that the valve of the _Cronia_ 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 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 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 coralline, took a year (which is
a low estimate enough), the accumulation of the inch of chalk must have
taken more than a year: and the deposit of a thousand feet of chalk must,
consequently, have taken more than twelve thousand years.
The foundation of all this calculation is, of course, a knowledge of the
length of time the _Crania_ and the coralline needed to attain 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 during the life of a _Crania_; and, on any probable
estimate of the length of that life, the chalk period 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 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
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 made, in
various parts of Western Europe, of flint implements, obviously worked
into shape by human hands, under circumstances which show conclusively
that man is a very ancient denizen of these regions. It has been proved
that the whole populations of Europe, whose existence has been revealed
to us 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 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 traditions of the
oldest historical nations. The name and fame of 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 of antiquity.
But, if 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 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 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 by the same agency as that which has planted blocks of
syenite from Norway 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 is not strictly true. Interposed between the
chalk and the drift is a comparatively insignificant layer, containing
vegetable 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 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 bolls of
some of these trees are from two to three feet in diameter, it is no less
clear that the dry land thus formed remained in the same condition 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 additional
evidence to the same effect is afforded by the abundant remains of
elephants, rhinoceroses, hippopotamuses, and other great wild beasts,
which it has yielded to the zealous search of such men as the Rev. Mr.
Gunn. When you look at such a collection as he has formed, and bethink
you that these elephantine bones did veritably carry their owners about,
and 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.
Thus there is a writing upon the wall of cliffs at Cromer, and whoso runs
may read it. It tells us, with an authority which 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 of which have rejoiced your geologists. How long it remained in
that condition cannot be said; but "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 and dry 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 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.
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 of men, that the chalk is vastly older than Adam himself.
The Book 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 geographical position of Eden has greatly vexed the
spirits of the learned in such matters, but there is one point respecting
which, 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. 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 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 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 indefinitely increase its
quantity, compels you to believe that the earth, from the time of the
chalk to the present day, has been the theatre of a series of changes as
vast in their amount, as they were slow in their progress. The area on
which we stand has been first sea and then land, for at least four
alternations; and has remained in each of these conditions for a period
of great length.
Nor have these wonderful metamorphoses of sea into land, and of land into
sea, been confined to one corner of England. During the chalk period, or
"cretaceous 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 since the chalk was deposited,
and the cretaceous sea flowed over the sites of Sinai and Ararat. All
this is certain, because 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 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
of time, represented elsewhere by thousands of feet of rock, is not
indicated at Cromer.