the world. If the sea were drained off, you might drive a wagon all
the way from Valentia, on the west coast of Ireland, to Trinity Bay in
Newfoundland. And, except upon one sharp incline about two hundred
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 two hundred miles to the point at which the bottom is now
covered by seventeen hundred 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 ten thousand to fifteen thousand 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 three hundred 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 grayish
white friable substance. You can write with this on a black-board, 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 Globigerinæ 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 Globigerinæ of the chalk--it is unnecessary to speak of them.
Globigerinæ 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 Globigerina 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 Giobigerinæ 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 Globigerinæ of the
Atlantic sea-bottom do not live and die where they are found.
[Illustration: DIATOM OOZE DREDGED FROM A DEPTH OF 1950 FEET.
(Magnified nearly 300 diameters.)]
As I have mentioned, the soundings from the great Atlantic plain are
almost entirely made up of Globigerinæ, 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 siliceous bodies belong partly
to the lowly vegetable organisms which are called Diatomaceæ, 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 siliceous 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.
[Illustration: RADIOLARIA. (_a._ Natural size. _b._ One-third natural
size.)]
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 Globigerinæ 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 Globigerinæ 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 Globigerinæ, in
proportion to other organisms of like kind, increases with the depth
of the sea; and that deep-water Globigerinæ are larger than those
which live in the 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.[1]
[Footnote 1: During the cruise of H.M.S. Bull-dog, 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 1260
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 Globigerinæ. This discovery removes all
objections to the existence of living Globigerinæ 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 Globigerinæ live and die
where they are found.]
However, the important points for us are, that the living Globigerinæ
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 Globigerinæ 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 mere powder and waste of Globigerinæ, 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 he 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 soundings, contains these mysterious
coccoliths and coccospheres. Here was a further and a most interesting
confirmation, from internal evidence, of the essential identity of the
chalk with modern deep-sea mud. Globigerinæ, 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.[2]
[Footnote 2: 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 1/1600th), and no longer doubt that they
are produced by independent organisms, which, like the Globigerinæ,
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
Globigerinæ; 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 Globigerinæ 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 Globigerinæ, 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.
[Illustration: UPPER SILURIAN CORALS AND CRUSTACEANS.]
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.
[Illustration: CRETACEOUS NAUTILUS.]
No less certain is it that the time during which the countries we now
call southeast 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 the 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."
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 Globigeringæ. For the outward
face of the valve of a Crania, which is attached to a sea-urchin
(Micrastor), 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 imbedded in the mud.
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 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 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 old 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 seaboard 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 whose spoils 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.