DISCOURSES:
BIOLOGICAL & GEOLOGICAL
ESSAYS
BY
THOMAS H. HUXLEY
1894
PREFACE
The contents of the present volume, with three exceptions, are either
popular lectures, or addresses delivered to scientific bodies with which
I have been officially connected. I am not sure which gave me the more
trouble. For I have not been one of those fortunate persons who are able
to regard a popular lecture as a mere _hors d'oeuvre_, unworthy of being
ranked among the serious efforts of a philosopher; and who keep their
fame as scientific hierophants unsullied by attempts--at least of the
successful sort--to be understanded of the people.
On the contrary, I found that the task of putting the truths learned in
the field, the laboratory and the museum, into language which, without
bating a jot of scientific accuracy shall be generally intelligible,
taxed such scientific and literary faculty as I possessed to the
uttermost; indeed my experience has furnished me with no better
corrective of the tendency to scholastic pedantry which besets all those
who are absorbed in pursuits remote from the common ways of men, and
become habituated to think and speak in the technical dialect of their
own little world, as if there were no other.
If the popular lecture thus, as I believe, finds one moiety of its
justification in the self-discipline of the lecturer, it surely finds the
other half in its effect on the auditory. For though various sadly
comical experiences of the results of my own efforts have led me to
entertain a very moderate estimate of the purely intellectual value of
lectures; though I venture to doubt if more than one in ten of an average
audience carries away an accurate notion of what the speaker has been
driving at; yet is that not equally true of the oratory of the hustings,
of the House of Commons, and even of the pulpit?
Yet the children of this world are wise in their generation; and both the
politician and the priest are justified by results. The living voice has
an influence over human action altogether independent of the intellectual
worth of that which it utters. Many years ago, I was a guest at a great
City dinner. A famous orator, endowed with a voice of rare flexibility
and power; a born actor, ranging with ease through every part, from
refined comedy to tragic unction, was called upon to reply to a toast.
The orator was a very busy man, a charming conversationalist and by no
means despised a good dinner; and, I imagine, rose without having given a
thought to what he was going to say. The rhythmic roll of sound was
admirable, the gestures perfect, the earnestness impressive; nothing was
lacking save sense and, occasionally, grammar. When the speaker sat down
the applause was terrific and one of my neighbours was especially
enthusiastic. So when he had quieted down, I asked him what the orator
had said. And he could not tell me.
That sagacious person John Wesley, is reported to have replied to some
one who questioned the propriety of his adaptation of sacred words to
extremely secular airs, that he did not see why the Devil should be left
in possession of all the best tunes. And I do not see why science should
not turn to account the peculiarities of human nature thus exploited by
other agencies: all the more because science, by the nature of its being,
cannot desire to stir the passions, or profit by the weaknesses, of human
nature. The most zealous of popular lecturers can aim at nothing more
than the awakening of a sympathy for abstract truth, in those who do not
really follow his arguments; and of a desire to know more and better in
the few who do.
At the same time it must be admitted that the popularization of science,
whether by lecture or essay, has its drawbacks. Success in this
department has its perils for those who succeed. The "people who fail"
take their revenge, as we have recently had occasion to observe, by
ignoring all the rest of a man's work and glibly labelling him a more
popularizer. If the falsehood were not too glaring, they would say the
same of Faraday and Helmholtz and Kelvin.
On the other hand, of the affliction caused by persons who think that
what they have picked up from popular exposition qualifies them for
discussing the great problems of science, it may be said, as the Radical
toast said of the power of the Crown in bygone days, that it "has
increased, is increasing, and ought to be diminished." The oddities of
"English as she is spoke" might be abundantly paralleled by those of
"Science as she is misunderstood" in the sermon, the novel, and the
leading article; and a collection of the grotesque travesties of
scientific conceptions, in the shape of essays on such trifles as "the
Nature of Life" and the "Origin of All Things," which reach me, from time
to time, might well be bound up with them.
The tenth essay in this volume unfortunately brought me, I will not say
into collision, but into a position of critical remonstrance with regard
to some charges of physical heterodoxy, brought by my distinguished
friend Lord Kelvin, against British Geology. As President of the
Geological Society of London at that time (1869), I thought I might
venture to plead that we were not such heretics as we seemed to be; and
that, even if we were, recantation would not affect the question of
evolution.
I am glad to see that Lord Kelvin has just reprinted his reply to my
plea,[1] and I refer the reader to it. I shall not presume to question
anything, that on such ripe consideration, Lord Kelvin has to say upon
the physical problems involved. But I may remark that no one can have
asserted more strongly than I have done, the necessity of looking to
physics and mathematics, for help in regard to the earliest history of
the globe. (See pp. 108 and 109 of this volume.)
[Footnote 1: _Popular Lectures and Addresses._ II. Macmillan and Co.
1894.]
And I take the opportunity of repeating the opinion, that, whether what
we call geological time has the lower limit assigned to it by Lord
Kelvin, or the higher assumed by other philosophers; whether the germs of
all living things have originated in the globe itself, or whether they
have been imported on, or in, meteorites from without, the problem of the
origin of those successive Faunae and Florae of the earth, the existence of
which is fully demonstrated by paleontology remains exactly where it was.
For I think it will be admitted, that the germs brought to us by
meteorites, if any, were not ova of elephants, nor of crocodiles; not
cocoa-nuts nor acorns; not even eggs of shell-fish and corals; but only
those of the lowest forms of animal and vegetable life. Therefore, since
it is proved that, from a very remote epoch of geological time, the earth
has been peopled by a continual succession of the higher forms of animals
and plants, these either must have been created, or they have arisen by
evolution. And in respect of certain groups of animals, the well-
established facts of paleontology leave no rational doubt that they arose
by the latter method.
In the second place, there are no data whatever, which justify the
biologist in assigning any, even approximately definite, period of time,
either long or short, to the evolution of one species from another by the
process of variation and selection. In the ninth of the following essays,
I have taken pains to prove that the change of animals has gone on at
very different rates in different groups of living beings; that some
types have persisted with little change from the paleozoic epoch till
now, while others have changed rapidly within the limits of an epoch. In
1862 (see below p. 303, 304) in 1863 (vol. II., p. 461) and again in 1864
(ibid., p. 89-91) I argued, not as a matter of speculation, but, from
paleontological facts, the bearing of which I believe, up to that time,
had not been shown, that any adequate hypothesis of the causes of
evolution must be consistent with progression, stationariness and
retrogression, of the same type at different epochs; of different types
in the same epoch; and that Darwin's hypothesis fulfilled these
conditions.
According to that hypothesis, two factors are at work, variation and
selection. Next to nothing is known of the causes of the former process;
nothing whatever of the time required for the production of a certain
amount of deviation from the existing type. And, as respects selection,
which operates by extinguishing all but a small minority of variations,
we have not the slightest means of estimating the rapidity with which it
does its work. All that we are justified in saying is that the rate at
which it takes place may vary almost indefinitely. If the famous paint-
root of Florida, which kills white pigs but not black ones, were abundant
and certain in its action, black pigs might be substituted for white in
the course of two or three years. If, on the other hand, it was rare and
uncertain in action, the white pigs might linger on for centuries.
T.H. HUXLEY.
HODESLEA, EASTBOURNE,
_April, 1894._
CONTENTS
I
ON A PIECE OF CHALK [1868]
(A Lecture delivered to the working men of Norwich during the meeting of
the British Association.)
II
THE PROBLEMS OF THE DEEP SEA [1878]
III
ON SOME OF THE RESULTS OF THE EXPEDITION OF H.M.S. "CHALLENGER" [1875]
IV
YEAST [1871]
V
ON THE FORMATION OF COAL [1870]
(A Lecture delivered at the Philosophical Institute, Bradford.)
VI
ON THE BORDER TERRITORY BETWEEN THE ANIMAL AND THE VEGETABLE KINGDOMS
[1876]
(A Friday evening Lecture delivered at the Royal Institution.)
VII
A LOBSTER; OR, THE STUDY OF ZOOLOGY [1861]
(A Lecture delivered at the South Kensington Museum.)
VIII
BIOGENESIS AND ABIOGENESIS [1870]
(The Presidential Address to the Meeting of the British Association for
the Advancement of Science at Liverpool.)
IX
GEOLOGICAL CONTEMPORANEITY AND PERSISTENT TYPES OF LIFE [1862]
(Address to the Geological Society on behalf of the President by one of
the Secretaries.)
X
GEOLOGICAL REFORM [1869]
(Presidential Address to the Geological Society.)
XI
PALAEONTOLOGY AND THE DOCTRINE OF EVOLUTION [1870]
(Presidential Address to the Geological Society.)
I
ON A PIECE OF CHALK
[1868]
If a well were sunk at our feet in the midst of the city of Norwich, the
diggers would very soon find themselves at work in that white substance
almost too soft to be called rock, with which we are all familiar as
"chalk."
Not only here, but over the whole county of Norfolk, the well-sinker
might carry his shaft down many hundred feet without coming to the end of
the chalk; and, on the sea-coast, where the waves have pared away the
face of the land which breasts them, the scarped faces of the high cliffs
are often wholly formed of the same material. Northward, the chalk may be
followed as far as Yorkshire; on the south coast it appears abruptly in
the picturesque western bays of Dorset, and breaks into the Needles of
the Isle of Wight; while on the shores of Kent it supplies that long line
of white cliffs to which England owes her name of Albion.
Were the thin soil which covers it all washed away, a curved band of
white chalk, here broader, and there narrower, might be followed
diagonally across England from Lulworth in Dorset, to Flamborough Head in
Yorkshire--a distance of over 280 miles as the crow flies. From this band
to the North Sea, on the east, and the Channel, on the south, the chalk
is largely hidden by other deposits; but, except in the Weald of Kent and
Sussex, it enters into the very foundation of all the south-eastern
counties.
Attaining, as it does in some places, a thickness of more than a thousand
feet, the English chalk must be admitted to be a mass of considerable
magnitude. Nevertheless, it covers but an insignificant portion of the
whole area occupied by the chalk formation of the globe, much of which
has the same general characters as ours, and is found in detached
patches, some less, and others more extensive, than the English. Chalk
occurs in north-west Ireland; it stretches over a large part of France,--
the chalk which underlies Paris being, in fact, a continuation of that of
the London basin; it runs through Denmark and Central Europe, and extends
southward to North Africa; while eastward, it appears in the Crimea and
in Syria, and may be traced as far as the shores of the Sea of Aral, in
Central Asia. If all the points at which true chalk occurs were
circumscribed, they would lie within an irregular oval about 3,000 miles
in long diameter--the area of which would be as great as that of Europe,
and would many times exceed that of the largest existing inland sea--the
Mediterranean.
Thus the chalk is no unimportant element in the masonry of the earth's
crust, and it impresses a peculiar stamp, varying with the conditions to
which it is exposed, on the scenery of the districts in which it occurs.
The undulating downs and rounded coombs, covered with sweet-grassed turf,
of our inland chalk country, have a peacefully domestic and mutton-
suggesting prettiness, but can hardly be called either grand or
beautiful. But on our southern coasts, the wall-sided cliffs, many
hundred feet high, with vast needles and pinnacles standing out in the
sea, sharp and solitary enough to serve as perches for the wary
cormorant, confer a wonderful beauty and grandeur upon the chalk
headlands. And, in the East, chalk has its share in the formation of some
of the most venerable of mountain ranges, such as the Lebanon.
What is this wide-spread component of the surface of the earth? and
whence did it come?
You may think this no very hopeful inquiry. You may not unnaturally
suppose that the attempt to solve such problems as these can lead to no
result, save that of entangling the inquirer in vague speculations,
incapable of refutation and of verification. If such were really the
case, I should have selected some other subject than a "piece of chalk"
for my discourse. But, in truth, after much deliberation, I have been
unable to think of any topic which would so well enable me to lead you to
see how solid is the foundation upon which some of the most startling
conclusions of physical science rest.
A great chapter of the history of the world is written in the chalk. Few
passages in the history of man can be supported by such an overwhelming
mass of direct and indirect evidence as that which testifies to the truth
of the fragment of the history of the globe, which I hope to enable you
to read, with your own eyes, to-night. Let me add, that few chapters of
human history have a more profound significance for ourselves. I weigh my
words well when I assert, that the man who should know the true history
of the bit of chalk which every carpenter carries about in his breeches-
pocket, though ignorant of all other history, is likely, if he will think
his knowledge out to its ultimate results, to have a truer, and therefore
a better, conception of this wonderful universe, and of man's relation to
it, than the most learned student who is deep-read in the records of
humanity and ignorant of those of Nature.
The language of the chalk is not hard to learn, not nearly so hard as
Latin, if you only want to get at the broad features of the story it has
to tell; and I propose that we now set to work to spell that story out
together.
We all know that if we "burn" chalk the result is quicklime. Chalk, in
fact, is a compound of carbonic acid gas, and lime, and when you make it
very hot the carbonic acid flies away and the lime is left. By this
method of procedure we see the lime, but we do not see the carbonic acid.
If, on the other hand, you were to powder a little chalk and drop it into
a good deal of strong vinegar, there would be a great bubbling and
fizzing, and, finally, a clear liquid, in which no sign of chalk would
appear. Here you see the carbonic acid in the bubbles; the lime,
dissolved in the vinegar, vanishes from sight. There are a great many
other ways of showing that chalk is essentially nothing but carbonic acid
and quicklime. Chemists enunciate the result of all the experiments which
prove this, by stating that chalk is almost wholly composed of "carbonate
of lime."
It is desirable for us to start from the knowledge of this fact, though
it may not seem to help us very far towards what we seek. For carbonate
of lime is a widely-spread substance, and is met with under very various
conditions. All sorts of limestones are composed of more or less pure
carbonate of lime. The crust which is often deposited by waters which
have drained through limestone rocks, in the form of what are called
stalagmites and stalactites, is carbonate of lime. Or, to take a more
familiar example, the fur on the inside of a tea-kettle is carbonate of
lime; and, for anything chemistry tells us to the contrary, the chalk
might be a kind of gigantic fur upon the bottom of the earth-kettle,
which is kept pretty hot below.
Let us try another method of making the chalk tell us its own history. To
the unassisted eye chalk looks simply like a very loose and open kind of
stone. But it is possible to grind a slice of chalk down so thin that you
can see through it--until it is thin enough, in fact, to be examined with
any magnifying power that may be thought desirable. A thin slice of the
fur of a kettle might be made in the same way. If it were examined
microscopically, it would show itself to be a more or less distinctly
laminated mineral substance, and nothing more.
But the slice of chalk presents a totally different appearance when
placed under the microscope. The general mass of it is made up of very
minute granules; but, imbedded in this matrix, are innumerable bodies,
some smaller and some larger, but, on a rough average, not more than a
hundredth of an inch in diameter, having a well-defined shape and
structure. A cubic inch of some specimens of chalk may contain hundreds
of thousands of these bodies, compacted together with incalculable
millions of the granules.
The examination of a transparent slice gives a good notion of the manner
in which the components of the chalk are arranged, and of their relative
proportions. But, by rubbing up some chalk with a brush in water and then
pouring off the milky fluid, so as to obtain sediments of different
degrees of fineness, the granules and the minute rounded bodies may be
pretty well separated from one another, and submitted to microscopic
examination, either as opaque or as transparent objects. By combining the
views obtained in these various methods, each of the rounded bodies may
be proved to be a beautifully-constructed calcareous fabric, made up of a
number of chambers, communicating freely with one another. The chambered
bodies are of various forms. One of the commonest is something like a
badly-grown raspberry, being formed of a number of nearly globular
chambers of different sizes congregated together. It is called
_Globigerina_, and some specimens of chalk consist of little else than
_Globigerinoe_ and granules. Let us fix our attention upon the
_Globigerina_. It is the spoor of the game we are tracking. If we can
learn what it is and what are the conditions of its existence, we shall
see our way to the origin and past history of the chalk.
A suggestion which may naturally enough present itself is, that these
curious bodies are the result of some process of aggregation which has
taken place in the carbonate of lime; that, just as in winter, the rime
on our windows simulates the most delicate and elegantly arborescent
foliage--proving that the mere mineral water may, under certain
conditions, assume the outward form of organic bodies--so this mineral
substance, carbonate of lime, hidden away in the bowels of the earth, has
taken the shape of these chambered bodies. I am not raising a merely
fanciful and unreal objection. Very learned men, in former days, have
even entertained the notion that all the formed things found in rocks are
of this nature; and if no such conception is at present held to be
admissible, it is because long and varied experience has now shown that
mineral matter never does assume the form and structure we find in
fossils. If any one were to try to persuade you that an oyster-shell
(which is also chiefly composed of carbonate of lime) had crystallized
out of sea-water, I suppose you would laugh at the absurdity. Your
laughter would be justified by the fact that all experience tends to show
that oyster-shells are formed by the agency of oysters, and in no other
way. And if there were no better reasons, we should be justified, on like
grounds, in believing that _Globigerina_ is not the product of anything
but vital activity.
Happily, however, better evidence in proof of the organic nature of the
_Globigerinoe_ than that of analogy is forthcoming. It so happens that
calcareous skeletons, exactly similar to the _Globigerinoe_ of the chalk,
are being formed, at the present moment, by minute living creatures,
which flourish in multitudes, literally more numerous than the sands of
the sea-shore, over a large extent of that part of the earth's surface
which is covered by the ocean.
The history of the discovery of these living _Globigerinoe_, and of the
part which they play in rock building, is singular enough. It is a
discovery which, like others of no less scientific importance, has
arisen, incidentally, out of work devoted to very different and
exceedingly practical interests. When men first took to the sea, they
speedily learned to look out for shoals and rocks; and the more the
burthen of their ships increased, the more imperatively necessary it
became for sailors to ascertain with precision the depth of the waters
they traversed. Out of this necessity grew the use of the lead and
sounding line; and, ultimately, marine-surveying, which is the recording
of the form of coasts and of the depth of the sea, as ascertained by the
sounding-lead, upon charts.
At the same time, it became desirable to ascertain and to indicate the
nature of the sea-bottom, since this circumstance greatly affects its
goodness as holding ground for anchors. Some ingenious tar, whose name
deserves a better fate than the oblivion into which it has fallen,
attained this object by "arming" the bottom of the lead with a lump of
grease, to which more or less of the sand or mud, or broken shells, as
the case might be, adhered, and was brought to the surface. But, however
well adapted such an apparatus might be for rough nautical purposes,
scientific accuracy could not be expected from the armed lead, and to
remedy its defects (especially when applied to sounding in great depths)
Lieut. Brooke, of the American Navy, some years ago invented a most
ingenious machine, by which a considerable portion of the superficial
layer of the sea-bottom can be scooped out and brought up from any depth
to which the lead descends. In 1853, Lieut. Brooke obtained mud from the
bottom of the North Atlantic, between Newfoundland and the Azores, at a
depth of more than 10,000 feet, or two miles, by the help of this
sounding apparatus. The specimens were sent for examination to Ehrenberg
of Berlin, and to Bailey of West Point, and those able microscopists
found that this deep-sea mud was almost entirely composed of the
skeletons of living organisms--the greater proportion of these being just
like the _Globigerinoe_ already known to occur in the chalk.
Thus far, the work had been carried on simply in the interests of
science, but Lieut. Brooke's method of sounding acquired a high
commercial value, when the enterprise of laying down the telegraph-cable
between this country and the United States was undertaken. For it became
a matter of immense importance to know, not only the depth of the sea
over the whole line along which the cable was to be laid, but the exact
nature of the bottom, so as to guard against chances of cutting or
fraying the strands of that costly rope. The Admiralty consequently
ordered Captain Dayman, an old friend and shipmate of mine, to ascertain
the depth over the whole line of the cable, and to bring back specimens
of the bottom. In former days, such a command as this might have sounded
very much like one of the impossible things which the young Prince in the
Fairy Tales is ordered to do before he can obtain the hand of the
Princess. However, in the months of June and July, 1857, my friend
performed the task assigned to him with great expedition and precision,
without, so far as I know, having met with any reward of that kind. The
specimens or Atlantic mud which he procured were sent to me to be
examined and reported upon.[1]
[Footnote 1: See Appendix to Captain Dayman's _Deep-sea Soundings in the
North Atlantic Ocean between Ireland and Newfoundland, made in H.M.S.
"Cyclops_." Published by order of the Lords Commissioners of the
Admiralty, 1858. They have since formed the subject of an elaborate
Memoir by Messrs. Parker and Jones, published in the _Philosophical
Transactions_ for 1865.]
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.