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    <h1>
      CORAL AND CORAL REEFS
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    <h2>
      by Thomas H. Huxley
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      <br /> <a href="#linknote-1" name="linknoteref-1" id="linknoteref-1"><small>[1]</small></a>
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    <p>
      THE subject upon which I wish to address you to-night is the structure and
      origin of Coral and Coral Reefs. Under the head of "coral" there are
      included two very different things; one of them is that substance which I
      imagine a great number of us have champed when we were very much younger
      than we are now,&mdash;the common red coral, which is used so much, as you
      know, for the edification and the delectation of children of tender years,
      and is also employed for the purposes of ornament for those who are much
      older, and as some think might know better. The other kind of coral is a
      very different substance; it may for distinction's sake be called the
      white coral; it is a material which most assuredly not the hardest-hearted
      of baby farmers would give to a baby to chew, and it is a substance which
      is to be seen only in the cabinets of curious persons, or in museums, or,
      may be, over the mantelpieces of sea-faring men. But although the red
      coral, as I have mentioned to you, has access to the very best society;
      and although the white coral is comparatively a despised product, yet in
      this, as in many other cases, the humbler thing is in reality the greater;
      the amount of work which is done in the world by the white coral being
      absolutely infinite compared with that effected by its delicate and
      pampered namesake. Each of these substances, the white coral and the red,
      however, has a relationship to the other. They are, in a zoological sense,
      cousins, each of them being formed by the same kind of animals in what is
      substantially the same way. Each of these bodies is, in fact, the hard
      skeleton of a very curious and a very simple animal, more comparable to
      the bones of such animals as ourselves than to the shells of oysters or
      creatures of that kind; for it is the hardening of the internal tissue of
      the creature, of its internal substance, by the deposit in the body of a
      material which is exceedingly common, not only in fresh but in sea water,
      and which is specially abundant in those waters which we know as "hard,"
      those waters, for example, which leave a "fur" upon the bottom of a
      tea-kettle. This "fur" is carbonate of lime, the same sort of substance as
      limestone and chalk. That material is contained in solution in sea water,
      and it is out of the sea water in which these coral creatures live that
      they get the lime which is needed for the forming of their hard skeleton.
    </p>
    <p>
      But now what manner of creatures are these which form these hard
      skeletons? I dare say that in these days of keeping aquaria, of locomotion
      to the sea-side, most of those whom I am addressing may have seen one of
      those creatures which used to be known as the "sea anemone," receiving
      that name on account of its general resemblance, in a rough sort of way,
      to the flower which is known as the "anemone"; but being a thing which
      lives in the sea, it was qualified as the "sea anemone." Well, then, you
      must suppose a body shaped like a short cylinder, the top cut off, and in
      the top a hole rather oval than round. All round this aperture, which is
      the mouth, imagine that there are placed a number of feelers forming a
      circle. The cavity of the mouth leads into a sort of stomach, which is
      very unlike those of the higher animals, in the circumstance that it opens
      at the lower end into a cavity of the body, and all the digested matter,
      converted into nourishment, is thus distributed through the rest of the
      body. That is the general structure of one of these sea anemones. If you
      touch it it contracts immediately into a heap. It looks at first quite
      like a flower in the sea, but if you touch it you find that it exhibits
      all the peculiarities of a living animal; and if anything which can serve
      as its prey comes near its tentacles, it closes them round it and sucks
      the material into its stomach and there digests it and turns it to the
      account of its own body.
    </p>
    <p>
      These creatures are very voracious, and not at all particular what they
      seize; and sometimes it may be that they lay hold of a shellfish which is
      far too big to be packed into that interior cavity, and, of course, in any
      ordinary animal a proceeding of this kind would give rise to a very severe
      fit of indigestion. But this is by no means the case in the sea anemone,
      because when digestive difficulties of this kind arise he gets out of them
      by splitting himself in two; and then each half builds itself up into a
      fresh creature, and you have two polypes where there was previously one,
      and the bone which stuck in the way lying between them! Not only can these
      creatures multiply in this fashion, but they can multiply by buds. A bud
      will grow out of the side of the body (I am not speaking of the common sea
      anemone, but of allied creatures) just like the bud of a plant, and that
      will fashion itself into a creature just like the parent. There are some
      of them in which these buds remain connected together, and you will soon
      see what would be the result of that. If I make a bud grow out here, and
      another on the opposite side, and each fashions itself into a new polype,
      the practical effect will be that before long you will see a single polype
      converted into a sort of tree or bush of polypes. And these will all
      remain associated together, like a kind of co-operative store, which is a
      thing I believe you understand very well here,&mdash;each mouth will help
      to feed the body and each part of the body help to support the
      multifarious mouths. I think that is as good an example of a zoological
      co-operative store as you can well have. Such are these wonderful
      creatures. But they are capable not only of multiplying in this way, but
      in other ways, by having a more ordinary and regular kind of offspring.
      Little eggs are hatched and the young are passed out by the way of the
      mouth, and they go swimming about as little oval bodies covered with a
      very curious kind of hairlike processes. Each of these processes is
      capable of striking water like an oar; and the consequence is that the
      young creature is propelled through the water. So that you have the young
      polype floating about in this fashion, covered by its 'vibratile cilia',
      as these long filaments, which are capable of vibration are termed. And
      thus, although the polype itself may be a fixed creature unable to move
      about, it is able to spread its offspring over great areas. For these
      creatures not only propel themselves, but while swimming about in the sea
      for many hours, or perhaps days, it will be obvious that they must be
      carried hither and thither by the currents of the sea, which not
      unfrequently move at the rate of one or two miles an hour. Thus, in the
      course of a few days, the offspring of this stationary creature may be
      carried to a very great distance from its parent; and having been so
      carried it loses these organs by which it is propelled, and settles down
      upon the bottom of the sea and grows up again into the form and condition
      of its parents. So that if you suppose a single polype of this kind
      settled upon the bottom of the sea, it may by these various methods&mdash;that
      is to say, by cutting itself in two, which we call "fission," or by
      budding; or by sending out these swimming embryos,&mdash;multiply itself
      to an enormous extent, and give rise to thousands, or millions, of progeny
      in a comparatively short time; and these thousands, or millions, of
      progeny may cover a very large surface of the sea bottom; in fact, you
      will readily perceive that, give them time, and there is no limit to the
      surface which they may cover.
    </p>
    <p>
      Having understood thus far the general nature of these polypes, which are
      the fabricators both of the red and white coral, let us consider a little
      more particularly how the skeletons of the red coral and of the white
      coral are formed. The red coral polype perches upon the sea bottom, it
      then grows up into a sort of stem, and out of that stem there grow
      branches, each of which has its own polypes; and thus you have a kind of
      tree formed, every branch of the tree terminated by its polype. It is a
      tree, but at the end of the branches there are open mouths of polypes
      instead of flowers. Thus there is a common soft body connecting the whole,
      and as it grows up the soft body deposits in its interior a quantity of
      carbonate of lime, which acquires a beautiful red or flesh colour, and
      forms a kind of stem running through the whole, and it is that stem which
      is the red coral. The red coral grows principally at the bottom of the
      Mediterranean Sea, at very great depths, and the coral fishers, who are
      very adventurous seamen, take their drag nets, of a peculiar kind, roughly
      made, but efficient for their purpose, and drag them along the bottom of
      the sea to catch the branches of the red coral, which become entangled and
      are thus brought up to the surface. They are then allowed to putrefy, in
      order to get rid of the animal matter, and the red coral is the skeleton
      that is left.
    </p>
    <p>
      In the case of the white coral, the skeleton is more complete. In the red
      coral, the skeleton belongs to the whole; in the white coral there is a
      special skeleton for every one of these polypes in addition to that for
      the whole body. There is a skeleton formed in the body of each of them,
      like a cup divided by a number of radiating partitions towards the
      outside; and that cup is formed of carbonate of lime, only not stained
      red, as in the case of the red coral. And all these cups are joined
      together into a common branch, the result of which is the formation of a
      beautiful coral tree. This is a great mass of madrepore, and in the living
      state every one of the ends of these branches was terminated by a
      beautiful little polype, like a sea anemone, and all the skeleton was
      covered by a soft body which united the polypes together. You must
      understand that all this skeleton has been formed in the interior of the
      body, to suit the branched body of the polype mass, and that it is as much
      its skeleton as our own bones are our skeleton. In this next coral the
      creature which has formed the skeleton has divided itself as it grew, and
      consequently has formed a great expansion; but scattered all over this
      surface there were polype bodies like those I previously described. Again,
      when this great cup was alive, the whole surface was covered with a
      beautiful body upon which were set innumerable small polype flowers, if we
      may so call them, often brilliantly coloured; and the whole cup was built
      up in the same fashion by the deposit of carbonate of lime in the interior
      of the combined polype body, formed by budding and by fission in the way I
      described. You will perceive that there is no necessary limit to this
      process. There is no reason why we should not have coral three or four
      times as big; and there are certain creatures of this kind that do
      fabricate very large masses, or half spheres several feet in diameter.
      Thus the activity of these animals in separating carbonate of lime from
      the sea and building it up into definite shapes is very considerable
      indeed.
    </p>
    <p>
      Now I think I have said sufficient&mdash;as much as I can without taking
      you into technical details, of the general nature of these creatures which
      form coral. The animals which form coral are scattered over the seas of
      all countries in the world. The red coral is comparatively limited, but
      the polypes which form the white coral are widely scattered. There are
      some of them which remain single, or which give rise to only small
      accumulations; and the skeletons of these, as they die, accumulate upon
      the bottom of the sea, but they do not come to much; they are washed about
      and do not adhere together, but become mixed up with the mud of the sea.
      But there are certain parts of the world in which the coral polypes which
      live and grow are of a kind which remain, adhere together, and form great
      masses. They differ from the ordinary polypes just in the same way as
      those plants which form a peat-bog or meadow-turf differ from ordinary
      plants. They have a habit of growing together in masses in the same place;
      they are what we call "gregarious" things; and the consequence of this is,
      that as they die and leave their skeletons, those skeletons form a
      considerable solid aggregation at the bottom of the sea, and other polypes
      perch upon them, and begin building upon them, and so by degrees a great
      mass is formed. And just as we know there are some ancient cities in which
      you have a British city, and over that the foundations of a Roman city;
      and over that a Saxon city, and over that again a modern city, so in these
      localities of which I am speaking, you have the accumulations of the
      foundations of the houses, if I may use the term, of nation after nation
      of these coral polypes; and these accumulations may cover a very
      considerable space, and may rise in the course of time from the bottom to
      the surface of the sea.
    </p>
    <p>
      Mariners have a name which they apply to all sorts of obstacles consisting
      of hard and rocky matter which comes in their way in the course of their
      navigation; they call such obstacles "reefs," and they have long been in
      the habit of calling the particular kind of reef, which is formed by the
      accumulation of the skeletons of dead corals, by the name of "coral
      reefs," therefore, those parts of the world in which these accumulations
      occur have been termed by them "coral reef areas," or regions in which
      coral reefs are found. There is a very notable example of a simple coral
      reef about the island of Mauritius, which I dare say you all know, lies in
      the middle of the Indian Ocean. It is a very considerable and beautiful
      island, and is surrounded on all sides by a mass of coral, which has been
      formed in the way I have described; so that if you could get upon the top
      of one of the peaks of the island, and look down upon the Indian Ocean,
      you would see that the beach round the Island was continued outward by a
      kind of shallow terrace, which is covered by the sea, and where the sea is
      quite shallow; and at a distance varying from three-quarters of a mile to
      a mile and a half from the proper beach, you would see a line of foam or
      surf which looks most beautiful in contrast with the bright green water in
      the inside, and the deep blue of the sea beyond. That line of surf
      indicates the point at which the waters of the ocean are breaking upon the
      coral reef which surrounds the island. You see it sweep round the island
      upon all sides, except where a river may chance to come down, and that
      always makes a gap in the shore.
    </p>
    <p>
      There are two or three points which I wish to bring clearly before your
      notice about such a reef as this. In the first place, you perceive it
      forms a kind of fringe round the island, and is therefore called a
      "fringing reef." In the next place, if you go out in a boat, and take
      soundings at the edge of the reef, you find that the depth of the water is
      not more than from 20 to 25 fathoms&mdash;that is about 120 to 150 feet.
      Outside that point you come to the natural sea bottom; but all inside that
      depth is coral, built up from the bottom by the accumulation of the
      skeletons of innumerable generations of coral polypes. So that you see the
      coral forms a very considerable rampart round the island. What the exact
      circumference may be I do not remember, but it cannot be less than 100
      miles, and the outward height of this wall of coral rock nowhere amounts
      to less than about 100 or 150 feet.
    </p>
    <p>
      When the outward face of the reef is examined, you find that the upper
      edge, which is exposed to the wash of the sea, and all the seaward face,
      is covered with those living plant-like flowers which I have described to
      you. They are the coral polypes which grow, flourish, and add to the mass
      of calcareous matter which already forms the reef. But towards the lower
      part of the reef, at a depth of about 120 feet, these creatures are less
      active, and fewer of them at work; and at greater depths than that you
      find no living coral polype at all; and it may be laid down as a rule,
      derived from very extensive observation, that these reef-building corals
      cannot live in a greater depth of water than about 120 to 150 feet. I beg
      you to recollect that fact, because it is one I shall have to come back to
      by and by, and to show to what very curious consequences that rule leads.
      Well then, coming back to the margin of the reef, you find that part of it
      which lies just within the surf to be coated by a very curious plant, a
      sort of seaweed, which contains in its substance a very great deal of
      carbonate of lime, and looks almost like rock; this is what is called the
      nulli pore. More towards the land, we come to the shallow water upon the
      inside of the reef, which has a particular name, derived from the Spanish
      or the Portuguese&mdash;it is called a "lagoon," or lake. In this lagoon
      there is comparatively little living coral; the bottom of it is formed of
      coral mud. If we pounded this coral in water, it would be converted into
      calcareous mud, and the waves during storms do for the coral skeletons
      exactly what we might do for this coral in a mortar; the waves tear off
      great fragments and crush them with prodigious force, until they are
      ground into the merest powder, and that powder is washed into the interior
      of the lagoon, and forms a muddy coating at the bottom. Beside that there
      are a great many animals that prey upon the coral&mdash;fishes, worms, and
      creatures of that kind, and all these, by their digestive processes,
      reduce the coral to the same state, and contribute a very important
      element to this fine mud. The living coral found in the lagoon, is not the
      reef building coral; it does not give rise to the same massive skeletons.
      As you go in a boat over these shallow pools, you see these beautiful
      things, coloured red, blue, green, and all colours, building their houses;
      but these are mere tenements, and not to be compared in magnitude and
      importance to the masses which are built by the reef-builders themselves.
      Now such a structure as this is what is termed a "fringing reef." You meet
      with fringing reefs of this kind not only in the Mauritius, but in a
      number of other parts of the world. If these were the only reefs to be
      seen anywhere, the problem of the formation of coral reefs would never
      have been a difficult one. Nothing can be easier than to understand how
      there must have been a time when the coral polypes came and settled on the
      shores of this island, everywhere within the 20 to 25 fathom line, and
      how, having perched there, they gradually grew until they built up the
      reef.
    </p>
    <p>
      But these are by no means the only sort of coral reefs in the world; on
      the contrary, there are very large areas, not only of the Indian ocean,
      but of the Pacific, in which many many thousands of square miles are
      covered either with a peculiar kind of reef, which is called the
      "encircling reef," or by a still more curious reef which goes by the name
      of the "atoll." There is a very good picture, which Professor Roscoe has
      been kind enough to prepare for me, of one of these atolls, which will
      enable you to form a notion of it as a landscape. You have in the
      foreground the waters of the Pacific. You must fancy yourself in the
      middle of the great ocean, and you will perceive that there is an almost
      circular island, with a low beach, which is formed entirely of coral sand;
      growing upon that beach you have vegetation, which takes, of course, the
      shape of the circular land; and then, in the interior of the circle, there
      is a pool of water, which is not very deep&mdash;probably in this case not
      more than eight or nine fathoms&mdash;and which forms a strange and
      beautiful contrast to the deep blue water outside. This circular island,
      or atoll, with a lagoon in the middle, is not a complete circle; upon one
      side of it there is a break, exactly like the entrance into a dock; and,
      as a matter of course, these circular islets, or atolls, form most
      efficient break-waters, for if you can only get inside your ship is in
      perfect safety, with admirable anchorage in the interior. If the ship were
      lying within a mile of that beach, the water would be one or two thousand
      feet deep; therefore, a section of that atoll, with the soundings as deep
      as this all round, would give you the notion of a great cone, cut off at
      the top, and with a shallow cup in the middle of it. Now, what a very
      singular fact this is, that we should have rising from the bottom of the
      deep ocean a great pyramid, beside which all human pyramids sink into the
      most utter insignificance! These singular coral limestone structures are
      very beautiful, especially when crowned with cocoa-nut trees. There you
      see the long line of land, covered with vegetation&mdash;cocoa-nut trees&mdash;and
      you have the sea upon the inner and outer sides, with a vessel very
      comfortably riding at anchor. That is one of the remarkable forms of reef
      in the Pacific. Another is a sort of half-way house, between the atoll and
      the fringing reef; it is what is called an "encircling reef." In this case
      you see an Island rising out of the sea, and at two or three miles
      distance, or more, and separated by a deep channel, which may be eight to
      twelve fathoms deep, there is a reef, which encircles it like a great
      girdle; and outside that again the water is one or two thousand feet deep.
      I spent three or four years of my life in cruising about a modification of
      one of these encircling reefs, called a "barrier reef," upon the east
      coast of Australia&mdash;one of the most wonderful accumulations of coral
      rock in the world. It is about 1,100 miles long, and varies in width from
      one or two to many miles. It is separated from the coast of Australia by a
      channel of about 25 fathoms deep; while outside, looking toward America,
      the water is two or three thousand feet deep at a mile from the edge of
      the reef. This is an accumulation of limestone rock, built up by corals,
      to which we have no parallel anywhere else. Imagine to yourself a heap of
      this material more than one thousand miles long, and several miles wide.
      That is a barrier reef; but a barrier reef is merely as it were a fragment
      of an encircling reef running parallel to the coast of a great continent.
    </p>
    <p>
      I told you that the polypes which built these reefs were not able to live
      at a greater depth than 20 to 25 fathoms of water; and that is the reason
      why the fringing reef goes no farther from the land than it does. And for
      the same reason, if the Pacific could be laid bare we should have a most
      singular spectacle. There would be a number of mountains with truncated
      tops scattered over it, and those mountains would have an appearance just
      the very reverse of that presented by the mountains we see on shore. You
      know that the mountains on shore are covered with vegetation at their
      bases, while their tops are barren or covered with snow; but these
      mountains would be perfectly bare at their bases, and all round their tops
      they would be covered with a beautiful vegetation of coral polypes. And
      not only would this be the case, but we should find that for a
      considerable distance down, all the material of these atoll and encircling
      reefs was built up of precisely the same coral rock as the fringing reef.
      That is to say, you have an enormous mass of coral rock at a depth below
      the surface of the water where we know perfectly well that the coral
      animals could not have lived to form it. When those two facts were first
      put together, naturalists were quite as much puzzled as I daresay you are,
      at present, to understand how these two seeming contradictions could be
      reconciled; and all sorts of odd hypotheses were resorted to. It was
      supposed that the coral did not extend so far down, but that there was a
      great chain of submarine mountains stretching through the Pacific, and
      that the coral had grown upon them. But only fancy what supposition that
      was, for you would have to imagine that there was a chain of mountains a
      thousand miles or more long, and that the top of every mountain came
      within 20 fathoms of the surface of the sea, and neither rose above nor
      sunk beneath that level. That is highly improbable: such a chain of
      mountains was never known. Then how can you possibly account for the
      curious circular form of the atolls by any supposition of this kind? I
      believe there was some one who imagined that all these mountains were
      volcanoes, and that the reefs had grown round the tops of the craters, so
      we all stuck fast. I may say "we," though it was rather before my time.
      And when we all stick fast, it is just the use of a man of genius that he
      comes and shows us the meaning of the thing. He generally gives an
      explanation which is so ridiculously simple that everybody is ashamed that
      he did not find it out before; and the way such a discoverer is often
      rewarded is by finding out that some one had made the discovery before
      him! I do not mean to say that it was so in this particular instance,
      because the great man who played the part of Columbus and the egg on this
      occasion had, I believe, always had the full credit which he so well
      deserves. The discoverer of the key to these problems was a man whose name
      you know very well in connection with other matters, and I should not
      wonder if some of you have heard it said that he was a superficial kind of
      person who did not know much about the subject on which he writes. He was
      Mr. Darwin, and this brilliant discovery of his was made public thirty
      years ago, long before he became the celebrated man he now is; and it was
      one of the most singular instances of that astonishing sagacity which he
      possesses of drawing consequences by way of deduction from simple
      principles of natural science&mdash;a power which has served him in good
      stead on other occasions. Well, Mr. Darwin, looking at these curious
      difficulties and having that sort of knowledge of natural phenomena in
      general, without which he could not have made a step towards the solution
      of the problem, said to himself&mdash;"It is perfectly clear that the
      coral which forms the base of the atolls and fringing reefs could not
      possibly have been formed there if the level of the sea has always been
      exactly where it is now, for we know for certain that these polypes cannot
      build at a greater depth than 20 to 25 fathoms, and here we find them at
      50 to 100 fathoms."
    </p>
    <p>
      That was the first point to make clear. The second point to deal with was&mdash;if
      the polypes cannot have built there while the level of the sea has
      remained stationary, then one of two things must have happened&mdash;either
      the sea has gone up, or the land has gone down.
    </p>
    <p>
      There is no escape from one of these two alternatives. Now the objections
      to the notion of the sea having gone up are very considerable indeed; for
      you will readily perceive that the sea could not possibly have risen a
      thousand feet in the Pacific without rising pretty much the same distance
      everywhere else; and if it had risen that height everywhere else since the
      reefs began to be formed, the geography of the world in general must have
      been very different indeed, at that time, from what it is now. And we have
      very good means of knowing that any such rise as this certainly has not
      taken place in the level of the sea since the time that the corals have
      been building their houses. And so the only other alternative was to
      suppose that the land had gone down, and at so slow a rate that the corals
      were able to grow upward as fast as it went downward. You will see at once
      that this is the solution of the mystery, and nothing can be simpler or
      more obvious when you come to think about it. Suppose we start with a
      coral sea and put in the middle of it an island such as the Mauritius. Now
      let the coral polypes come and perch on the shore and build a fringing
      reef, which will stop when they come to 20 or 25 fathoms, and you will
      have a fringing reef like that round the island in the illustration. So
      long as the land remains stationary, so long as it does not descend so
      long will that reef be unable to get any further out, because the moment
      the polype embryos try to get below they die. But now suppose that the
      land sinks very gradually indeed. Let it subside by slow degrees, until
      the mountain peak, which we have in the middle of it, alone projects
      beyond the sea level. The fringing reef would be carried down also; but we
      suppose that the sinking is so slow that the coral polypes are able to
      grow up as fast as the land is carried down; consequently they will add
      layer upon layer until they form a deep cup, because the inner part of the
      reef grows much more slowly than the outer part. Thus you have the reef
      forming a bed thicker upon the flanks of the island; but the edge of the
      reef will be very much further out from the land, and the lagoon will be
      many times deeper; in short, your fringing reef will be converted into an
      encircling reef. And if, instead of this being an island, it were a great
      continent like Australia, then you will have the phenomenon of a barrier
      reef which I have described. The barrier reef of Australia was originally
      a fringing reef; the land has gone slowly down; the consequence is the
      lagoon has deepened until its depth is now 25 fathoms and the corals have
      grown up at the outer edge until you have that prodigious accumulation
      which forms the barrier reef at present. Now let this process go on
      further still; let us take the land a further step down, so as to submerge
      even the peak. The coral, still growing up, will cover the surface of the
      land, and you will have an atoll reef; that is to say, a more or less
      circular or oval ring of coral rock with a lagoon in the middle. Thus you
      see that every peculiarity and phenomenon of these different forms of
      coral reef was explained at once by the simplest of all possible
      suppositions, namely, by supposing that the land has gone down at a rate
      not greater than that at which the coral polypes have grown up. You
      explain a Fringing Reef as a reef which is formed round land comparatively
      stationary; an Encircling Reef as one which is formed round land going
      down; and an Atoll as a reef formed upon land gone down; and the thing is
      so simple that a child may understand it when it is once explained.
    </p>
    <p>
      But this would by no means satisfy the conditions of a scientific
      hypothesis. No man who is cautious would dream of trusting to an
      explanation of this kind simply because it explained one particular set of
      facts. Before you can possibly be safe in dealing with Nature&mdash;who is
      very properly made of the feminine gender, on account of the astonishing
      tricks which she plays upon her admirers!&mdash;I say before you can be
      safe in dealing with Nature, you must get two or three kinds of cross
      proofs, so as to make sure not only that your hypothesis fits that
      particular set of facts, but that it is not contradicted by some other set
      of facts which is just as clear and certain. And it so happens, that in
      this case Mr. Darwin supplied the cross proofs as well as the immediate
      evidence. You have all heard of volcanoes, those wonderful vents in the
      surface of the earth out of which pour masses of lava, cinders and ashes,
      and the like. Now, it is a matter of observation and experience that all
      volcanoes are placed in areas in which the surface of the earth is
      undergoing elevation, or at any rate is stationary; they are not placed in
      parts of the world in which the level of the land is being lowered. They
      are all indications of a great subterranean activity, of a something being
      pushed up, and therefore naturally the land either gives way and lets it
      come through, or else is raised up by its violence. And so Mr. Darwin,
      being desirous not to merely put out a flashy hypothesis, but to get at
      the truth of the matter, said to himself, "If my notion of this matter is
      right, then atolls and encircling reefs, inasmuch as they are dependent
      upon subsidence, ought not to be found in company with volcanoes; and,
      'vice versa', volcanoes ought not to be found in company with atolls, but
      they ought to be found in company with fringing reefs." And if you turn to
      Mr. Darwin's great work upon the coral reefs, you will see a very
      beautiful chart of the world, which he prepared with great pains and
      labour, showing the distribution on the one hand of the reefs, and on the
      other of the volcanoes; you will find that in no case does the atoll
      accompany the volcano, or the volcano burst up among the atolls. It is
      most instructive to look at the great area of the Pacific on the map, and
      see the great masses of atolls forming in one region of it a most enormous
      belt, running from north-west to south-east; while the volcanoes, which
      are very numerous in that region, go round the margin, so that we can
      picture the Pacific to ourselves a section of a kind of very shallow basin&mdash;shallow
      in proportion to its width, with the atolls rising from the bottom of it,
      and at the margins the volcanoes. It is exactly as if you had taken a flat
      mass and lifted up the edges of it; the subterranean force which lifted up
      the edges shows itself in volcanoes, and as the edges have been raised,
      the middle part of the mass has gone down. In other words, the facts of
      physical geography precisely and exactly correspond with the hypothesis
      which accounts for the infinite varieties of coral reefs.
    </p>
    <p>
      One other point, before I conclude, about this matter. These reefs, as you
      have just perceived, are in a most singular and unexpected manner
      indications of physical changes of elevations and depressions going on
      upon the surface of the globe. I dare say it may have surprised you to
      hear me talk in this familiar sort of way of land going up and down; but
      it is one of the universal lessons of geology that the land is going down
      and going up, and has been going up and down, in all sorts of places and
      to all sorts of distances, through all recorded time. Geologists would be
      quite right in maintaining the seeming paradox that the stable thing in
      the world is the fluid sea and the shifting thing is the solid land. That
      may sound a very hard saying at first, but the more you look into geology,
      the more you will see ground for believing that it is not a mere paradox.
    </p>
    <p>
      In an unexpected manner, again, these reefs afford us not only an
      indication of change of place, but they afford an indication of lapse of
      time. The reef is a timekeeper of a very curious character; and you can
      easily understand why. The coral polype, like everything else, takes a
      certain time to grow to its full size; it does not do it in a minute; just
      as a child takes a certain time to grow into a man so does the embryo
      polype take time to grow into a perfect polype and form its skeleton.
      Consequently every particle of coral limestone is an expression of time.
      It must have taken a certain time to separate the lime from the sea water.
      It is not possible to arrive at an accurate computation of the time it
      must have taken to form these coral islands, because we lack the necessary
      data; but we can form a rough calculation, which leads to very curious and
      striking results. The computations of the rate at which corals grow are so
      exceedingly variable, that we must allow the widest possible margin for
      error; and it is better in this case to make the allowance upon the side
      of excess. I think that anybody who knows anything about the matter will
      tell you that I am making a computation far in excess of what is probable,
      if I say that an inch of coral limestone may be added to one of these
      reefs in the course of a year. I think most naturalists would be inclined
      to laugh at me for making such an assumption, and would put the growth at
      certainly not more than half that amount. But supposing it is so, what a
      very curious notion of the antiquity of some of these great living
      pyramids comes out by a very simple calculation. There is no doubt
      whatever that the sea faces of some of them are fully a thousand feet
      high, and if you take the reckoning of an inch a year, that will give you
      12,000 years for the age of that particular pyramid or cone of coral
      limestone; 12,000 long years have these creatures been labouring in
      conditions which must have been substantially the same as they are now,
      otherwise the polypes could not have continued their work. But I believe I
      very much understate both the height of some of these masses, and
      overstate the amount which these animals can form in the course of a year;
      so that you might very safely double the period as the time during which
      the Pacific Ocean, the general state of the climate, and the sea, and the
      temperature has been substantially what it is now; and yet that state of
      things which now obtains in the Pacific Ocean is the yesterday of the
      history of the life of the globe. Those pyramids of coral rock are built
      upon a foundation which is itself formed by the deposits which the
      geologist has to deal with. If we go back in time and search through the
      series of the rocks, we find at every age of the world's history which has
      yet been examined, accumulations of limestone, many of which have
      certainly been built up in just the same way as those coral reefs which
      are now forming the bottom of the Pacific Ocean. And even if we turn to
      the oldest periods of geologic history, although the nature of the
      materials is changed, although we cannot apply to them the same reasonings
      that we can to the existing corals, yet still there are vast masses of
      limestone formed of nothing else than the accumulations of the skeletons
      of similar animals, and testifying that even in those remote periods of
      the world's history, as now, the order of things implies that the earth
      had already endured for a period of which our ordinary standards of
      chronology give us not the slightest conception. In other words, the
      history of these coral reefs, traced out honestly and carefully, and with
      the same sort of reasoning that you would use in the ordinary affairs of
      life, testifies, like every fact that I know of, to the prodigious
      antiquity of the earth since it existed in a condition in the main similar
      to that in which it now is.
    </p>
    <p>
      <br /> <br />
    </p>
    <hr />
    <p>
      <br /> <br /> <a name="linknote-1" id="linknote-1">
      <!-- Note --></a>
    </p>
    <p class="foot">
      1 (<a href="#linknoteref-1">return</a>)<br /> [ A Lecture delivered in
      Manchester, November 4th, 1970.]
    </p>
    <p>
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