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+Project Gutenberg Etext of Coral and Coral Reefs, by T H Huxley
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+Title:  Coral and Coral Reefs
+
+Author:  Thomas H. Huxley
+
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+Project Gutenberg Etext of Coral and Coral Reefs, by T H Huxley
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+
+CORAL AND CORAL REEFS*
+
+by Thomas H. Huxley
+
+
+
+
+*[Foonote] A Lecture delivered in Manchester, November 4th, 1970.
+
+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,--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.
+
+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.
+
+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,--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--that is to say, by cutting itself
+in two, which we call "fission," or by budding; or by sending out these
+swimming embryos,--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.
+
+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.
+
+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.
+
+Now I think I have said sufficient--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.
+
+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.
+
+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--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.
+
+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--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--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.
+
+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--probably
+in this case not more than eight or nine fathoms--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--cocoa-nut trees--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--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.
+
+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--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--"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."
+
+That was the first point to make clear.  The second point to deal with
+was--if the polypes cannot have built there while the level of the sea
+has remained stationary, then one of two things must have
+happened--either the sea has gone up, or the land has gone down.
+
+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.
+
+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--who
+is very properly made of the feminine gender, on account of the
+astonishing tricks which she plays upon her admirers!--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--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.
+
+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.
+
+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.
+
+
+
+
+
+End of The Project Gutenberg Etext of Coral and Coral Reefs
+
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