Part 13

For, suppose the relative level of the sea to remain stationary, after a fringing reef has reached that distance from the land at which the depth of water amounts to one hundred and fifty feet. Then the reef cannot extend seaward by the migration of coral germs, because these coral germs would find the bottom of the sea to be too deep for them to live in. And the only manner in which the reef could extend outwards, would be by the gradual accumulation, at the foot of its seaward face, of a talus of coral fragments torn off by the violence of the waves, which talus might, in course of time, become high enough to bring its upper surface within the limits of coral growth, and in that manner provide a sort of factitious sea-bottom upon which the coral embryos might perch. If, on the other hand, the level of the sea were slowly and gradually lowered, it is clear that the parts of its bottom originally beyond the limit of coral growth would gradually be brought within the required distance of the surface, and thus the reef might be indefinitely extended. But this process would give rise neither to an encircling reef nor to an atoll, but to a broad belt of upheaved coral rock, increasing the dimensions of the dry land, and continuous seawards with the fresh fringing reef.

Suppose, however, that the sea-level rose instead of falling, at the same slow and gradual rate at which we know it to be rising in some parts of the world,--not more, in fact, than a few inches, or, at most, a foot or two, in a hundred years. Then, while the reef would be unable to extend itself seaward, the sea-bottom outside it being gradually more and more removed from the depth at which the life of the coral polypes is possible, it would be able to grow upwards as fast as the sea rose. But the growth would take place almost exclusively around the circumference of the reef, this being the only region in which the coral polypes would find the conditions favourable for their existence. The bottom of the lagoon would be raised, in the main, only by the coral debris and coral mud, formed in the manner already described; consequently, the margins of the reef would rise faster than the bottom, or, in other words, the lagoon would constantly become deeper. And, at the same time, it would gradually increase in breadth; as the rising sea, covering more of the land, would occupy a wider space between the edge of the reef and what remained of the land. Thus the rising sea would eventually convert a large island with a fringing reef into a small island surrounded by an encircling reef. And it will be obvious that when the rising of the sea has gone so far as completely to cover the highest points of the island, the reef will have passed into the condition of an atoll.

But how is it possible that the relative level of the land and sea should be altered to this extent? Clearly, only in one of two ways: either the sea must have risen over those areas which are now covered by atolls and encircling reefs; or, the land upon which the sea rests must have been depressed to a corresponding extent.

If the sea has risen, its rise must have taken place over the whole world simultaneously, and it must have risen to the same height over all parts of the coral zone. Grounds have been shown for the belief that the general level of the sea may have been different at different times; it has been suggested, for example, that the accumulation of ice about the poles during one of the cold periods of the earth's history necessarily implies a diminution in the volume of the sea proportioned to the amount of its water thus permanently locked up in the Arctic and Antarctic ice-cellars; while, in the warm periods, the greater or less disappearance of the polar ice-cap implies a corresponding addition of water to the ocean. And no doubt this reasoning must be admitted to be sound in principle; though it is very hard to say what practical effect the additions and subtractions thus made have had on the level of the ocean; inasmuch as such additions and subtractions might be either intensified or nullified, by contemporaneous changes in the level of the land. And no one has yet shown that any such great melting of polar ice, and consequent raising of the level of the water of the ocean, has taken place since the existing atolls began to be formed.

In the absence of any evidence that the sea has ever risen to the extent required to give rise to the encircling reefs and the atolls, Mr. Darwin adopted the opposite hypothesis, viz., that the land has undergone extensive and slow depression in those localities in which these structures exist.

It seems, at first, a startling paradox, to suppose that the land is less fixed than the sea; but that such is the case is the uniform testimony of geology. Beds of sandstone or limestone, thousands of feet thick, and all full of marine remains, occur in various parts of the earth's surface, and prove, beyond a doubt, that when these beds were formed, that portion of the sea-bottom which they then occupied underwent a slow and gradual depression to a distance which cannot have been less than the thickness of those beds, and may have been very much greater. In supposing, therefore, that the great areas of the Pacific and of the Indian Ocean, over which atolls and encircling reefs are found scattered, have undergone a depression of some hundreds, or, it may be, thousands of feet, Mr. Darwin made a supposition which had nothing forced or improbable, but was entirely in accordance with what we know to have taken place over similarly extensive areas, in other periods of the world's history. But Mr. Darwin subjected his hypothesis to an ingenious indirect test. If his view be correct, it is clear that neither atolls, nor encircling reefs, should be found in those portions of the ocean in which we have reason to believe, on independent grounds, that the sea-bottom has long been either stationary, or slowly rising. Now it is known that, as a general rule, the level of the land is either stationary, or is undergoing a slow upheaval, in the neighborhood of

## active volcanoes; and, therefore, neither atolls nor encircling reefs

ought to be found in regions in which volcanoes are numerous and active. And this turns out to be the case. Appended to Mr. Darwin's great work on coral reefs, there is a map on which atolls and encircling reefs are indicated by one colour, fringing reefs by another, and active volcanoes by a third. And it is at once obvious that the lines of active volcanoes lie around the margins of the areas occupied by the atolls and the encircling reefs. It is exactly as if the upheaving volcanic agencies had lifted up the edges of these great areas, while their centres had undergone a corresponding depression. An atoll area may, in short, be pictured as a kind of basin, the margins of which have been pushed up by the subterranean forces, to which the craters of the volcanoes have, at intervals, given vent.

Thus we must imagine the area of the Pacific now covered by the Polynesian Archipelago, as having been, at some former time, occupied by large islands, or, may be, by a great continent, with the ordinarily diversified surface of plain, and hill, and mountain chain. The shores of this great land were doubtless fringed by coral reefs; and, as it slowly underwent depression, the hilly regions, converted into islands, became, at first, surrounded by fringing reefs, and then, as depression went on, these became converted into encircling reefs, and these, finally, into atolls, until a maze of reefs and coral-girdled islets took the place of the original land masses.

Thus the atolls and the encircling reefs furnish us with clear, though indirect, evidence of changes in the physical geography of large parts of the earth's surface; and even, as my lamented friend, the late Professor Jukes,[124] has suggested, give us indications of the manner in which some of the most puzzling facts connected with the distribution of animals have been brought about. For example, Australia and New Guinea are separated by Torres Straits, a broad belt of sea one hundred or one hundred and twenty miles wide. Nevertheless, there is in many respects a curious resemblance between the land animals which inhabit New Guinea and the land animals which inhabit Australia. But, at the same time, the marine shellfish which are found in the shallow waters of the shores of New Guinea are quite different from those which are met with upon the coasts of Australia. Now, the eastern end of Torres Straits is full of atolls, which, in fact, form the northern termination of the Great Barrier Reef which skirts the eastern coast of Australia. It follows, therefore, that the eastern end of Torres Straits is an area of depression, and it is very possible, and on many grounds highly probable, that, in former times, Australia and New Guinea were directly connected together, and that Torres Straits did not exist. If this were the case, the existence of cassowaries and of marsupial quadrupeds, both in New Guinea and in Australia, becomes intelligible; while the difference between the littoral molluscs of the north and the south shores of Torres Straits is readily explained by the great probability that, when the depression in question took place, and what was, at first, an arm of the sea became converted into a strait separating Australia from New Guinea, the northern shore of this new sea became tenanted with marine animals from the north, while the southern shore was peopled by immigrants from the already existing marine Australian fauna.

Inasmuch as the growth of the reef depends upon that of successive generations of coral polypes, and as each generation takes a certain time to grow to its full size, and can only separate its calcareous skeleton from the water in which it lives at a certain rate, it is clear that the reefs are records not only of changes in physical geography, but of the lapse of time. It is by no means easy, however, to estimate the exact value of reef chronology, and the attempts which have been made to determine the rate at which a reef grows vertically have yielded anything but precise results. A cautious writer, Mr. Dana,[125] whose extensive study of corals and coral reefs makes him an eminently competent judge, states his conclusion in the following terms:--

"The rate of growth of the common branching madrepore is not over one and a half inches a year. As the branches are open, this would not be equivalent to more than half an inch in height of solid coral for the whole surface covered by the madrepore; and, as they are also porous, to not over three-eighths of an inch of solid limestone. But a coral plantation has large bare patches without corals, and the coral sands are widely distributed by currents, part of them to depths over one hundred feet where there are no living corals; not more than one-sixth of the surface of a reef region is, in fact, covered with growing species. This reduces the three-eighths to ONE-SIXTEENTH. Shells and other organic relics may contribute one-fourth as much as corals. At the outside, the average upward increase of the whole reef-ground per year would not exceed ONE-EIGHTH of an inch.

"Now some reefs are at least two thousand feet thick, which at one-eighth of an inch a year, corresponds to one hundred and ninety-two thousand years."*

* Dana, Manual of Geology, p. 591.

Halve, or quarter, this estimate if you will, in order to be certain of erring upon the right side, and still there remains a prodigious period during which the ancestors of existing coral polypes have been undisturbedly at work; and during which, therefore, the climatal conditions over the coral area must have been much what they are now.

And all this lapse of time has occurred within the most recent period of the history of the earth. The remains of reefs formed by coral polypes of different kinds from those which exist now, enter largely into the composition of the limestones of the Jurassic period;[126] and still more widely different coral polypes have contributed their quota to the vast thickness of the carboniferous and Devonian strata. Then as regards the latter group of rocks in America, the high authority already quoted tells us:--

"The Upper Helderberg period is eminently the coral reef period of the palaeozoic ages. Many of the rocks abound in coral, and are as truly coral reefs as the modern reefs of the Pacific. The corals are sometimes standing on the rocks in the position they had when growing: others are lying in fragments, as they were broken and heaped by the waves; and others were reduced to a compact limestone by the finer trituration before consolidation into rock. This compact variety is the most common kind among the coral reef rocks of the present seas; and it often contains but few distinct fossils, although formed in water that abounded in life. At the fall of the Ohio, near Louisville, there is a magnificent display of the old reef. Hemispherical Favosites, five or six feet in diameter, lie there nearly as perfect as when they were covered by their flowerlike polypes; and besides these, there are various branching corals, and a profusion of Cyathophyllia, or cup-corals."*

* Dana, Manual of Geology, p. 272.

Thus, in all the great periods of the earth's history of which we know anything, a part of the then living matter has had the form of polypes, competent to separate from the water of the sea the carbonate of lime necessary for their own skeletons. Grain by grain, and particle by

## particle, they have built up vast masses of rock, the thickness of which

is measured by hundreds of feet, and their area by thousands of square miles. The slow oscillations of the crust of the earth, producing great changes in the distribution of land and water, have often obliged the living matter of the coral-builders to shift the locality of its operations; and, by variation and adaptation to these modifications of condition, its forms have as often changed. The work it has done in the past is, for the most part, swept away, but fragments remain, and, if there were no other evidence, suffice to prove the general constancy of the operations of Nature in this world, through periods of almost inconceivable duration.

NOTES

AUTOBIOGRAPHY

[Footnote 1: Autobiography: Huxley's account of this sketch, written in 1889, is as follows: "A man who is bringing out a series of portraits of celebrities, with a sketch of their career attached, has bothered me out of my life for something to go with my portrait, and to escape the abominable bad taste of some of the notices, I have done that."]

[Footnote 2: pre-Boswellian epoch: the time before Boswell. James Boswell (1740-1795) wrote the famous Life of Samuel Johnson. Mr. Leslie Stephen declares that this book "became the first specimen of a new literary type." "It is a full-length portrait of a man's domestic life with enough picturesque detail to enable us to see him through the eyes of private friendship. . . ." A number of biographers since Boswell have imitated his method; and Leslie Stephen believes that "we owe it in some degree to his example that we have such delightful books as Lockhart's Life of Scott or Mr. Trevelyan's Life of Macaulay."]

[Footnote 3: "Bene qui latuit, bene vixit": from Ovid. He who has kept himself well hidden, has lived well.]

[Footnote 4: Prince George of Cambridge: the grandson of King George III, second Duke of Cambridge, and Commander-in-chief of the British Army.]

[Footnote 5: Mr. Herbert Spencer (1820--1903): a celebrated English philosopher and powerful advocate of the doctrine of evolution. Spencer is regarded as one of the most profound thinkers of modern times. He was one of Huxley's closest friends.]

[Footnote 6: in partibus infidelium: in the domain of the unbelievers.]

[Footnote 7: "sweet south upon a bed of violets." Cf. Twelfth Night, Act I, sc. I, l. 5.

O, it came o'er my ear like the sweet sound That breathes upon a bank of violets, Stealing and giving odour.

For the reading "sweet south" instead of "sweet sound," see Rolfe's edition of Twelfth Night.]

[Footnote 8: "Lehrjahre": apprenticeship.

Charing Cross School of Medicine: a school connected with the Charing Cross Hospital in the Strand, London.]

[Footnote 9: Nelson: Horatio Nelson, a celebrated English Admiral born in Norfolk, England, 1758, and died on board the Victory at Trafalgar, 1805. It was before the battle off Cape Trafalgar that Nelson hoisted his famous signal, "England expects every man will do his duty." Cf. Tennyson's Ode to the Duke of Wellington, stanza VI, for a famous tribute to Nelson.]

[Footnote 10: middies: abbreviated form for midshipmen.]

[Footnote 11: Suites a Buffon: sequels to Buffon. Buffon (1707-1781) was a French naturalist who wrote many volumes on science.]

[Footnote 12: Linnean Society: a scientific society formed in 1788 under the auspices of several fellows of the Royal Society.]

[Footnote 13: Royal Society: The Royal Society for Improving Natural Knowledge; the oldest scientific society in Great Britain, and one of the oldest in Europe. It was founded by Charles II, in 1660, its nucleus being an association of learned men already in existence. It is supposed to be identical with the Invisible College which Boyle mentions in 1646. It was incorporated under the name of The Royal Society in 1661. The publications of the Royal Society are called Philosophical Transactions. The society has close connection with the government, and has assisted the government in various important scientific undertakings among which may be mentioned Parry's North Pole expedition. The society also distributes $20,000 yearly for the promotion of scientific research.]

[Footnote 14: Rastignac: a character in Le Pere Goriot. At the close of the story Rastignac says, "A nous deux, maintenant":--Henceforth there is war between us.]

[Footnote 15: Pere Goriot: a novel of Balzac's with a plot similar to King Lear.]

[Footnote 16: Professor Tyndall (1820-1893): a distinguished British physicist and member of the Royal Society. He explored with Huxley the glaciers of Switzerland. His work in electricity, radiant heat, light and acoustics gave him a foremost place in science.]

[Footnote 17: Ecclesiastical spirit: the spirit manifested by the clergy of England in Huxley's time against the truths of science. The clergy considered scientific truth to be disastrous to religious truth. Huxley's attitude toward the teaching of religious truth is illuminated by this quotation, which he uses to explain his own position: "I have the fullest confidence that in the reading and explaining of the Bible, what the children will be taught will be the great truths of Christian Life and conduct, which all of us desire they should know, and that no effort will be made to cram into their poor little minds, theological dogmas which their tender age prevents them from understanding." Huxley defines his idea of a church as a place in which, "week by week, services should be devoted, not to the iteration of abstract propositions in theology, but to the setting before men's minds of an ideal of true, just and pure living; a place in which those who are weary of the burden of daily cares should find a moment's rest in the contemplation of the higher life which is possible for all, though attained by so few; a place in which the man of strife and of business should have time to think how small, after all, are the rewards he covets compared with peace and charity."]

[Footnote 18: New Reformation: Huxley writes: "We are in the midst of a gigantic movement greater than that which preceded and produced the Reformation, and really only the continuation of that movement. . . . But this organization will be the work of generations of men, and those who further it most will be those who teach men to rest in no lie, and to rest in no verbal delusion."]

ON THE ADVISABLENESS OF IMPROVING NATURAL KNOWLEDGE (1866)

[Footnote 19: On the Advisableness of Improving Natural Knowledge: from Method and Results: also published in Lay Sermons, Addresses and Reviews.]

For the history of the times mentioned in this essay, see Green's Short History of the English People.]

[Footnote 20: The very spot: St. Martin's Borough Hall and Public Library, on Charing Cross Road, near Trafalgar Square.]

[Footnote 21: Defoe (1661-1731): an English novelist and political writer. On account of his political writings Defoe was sentenced to stand in the pillory, and to be "imprisoned during the Queen's pleasure." During this imprisonment he wrote many articles. Later in life he wrote Robinson Crusoe, The Fortunes and Misfortunes of Moll Flanders, Journal of the Plague Year, and other books less well known.]

[Footnote 22: unholy cursing and crackling wit of the Rochesters and Sedleys: John Wilmot, the second Earl of Rochester, and Sir Charles Sedley, were both friends of Charles II, and were noted for biting wit and profligacy. Green, in his Short History of the English People, thus describes them: "Lord Rochester was a fashionable poet, and the titles of some of his poems are such as no pen of our day could copy. Sir Charles Sedley was a fashionable wit, and the foulness of his words made even the porters in the Covent Garden belt him from the balcony when he ventured to address them."]

[Footnote 23: Laud: Archbishop of Canterbury. Laud was born in 1573, and beheaded at London in 1645. He was throughout the reign of Charles I a staunch supporter of the King. He was impeached by the Long Parliament in 1640 and executed on Tower Hill, in 1645.]

[Footnote 24: selenography: the scientific study of the moon with special reference to its physical condition.]

[Footnote 25: Torricellian experiment: a reference to the discovery of the principle of the barometer by the Italian, Torricelli, in 1643.]

[Footnote 26: Sir Francis Bacon (1561-1626): Bacon endeavored to teach that civilization cannot be brought to a high point except as man applies himself to the study of the secrets of nature, and uses these discoveries for inventions which will give him power over his environment. The chief value of the work was that it called attention to the uses of induction and to the experimental study of facts. See Roger's A Student's History of Philosophy, page 243.]

[Footnote 27: The learned Dr. Wallis (1616-1703): Dr. Wallis is regarded as the greatest of Newton's predecessors in mathematical history. His works are numerous and are on a great variety of subjects. He was one of the first members of the Royal Society.]

[Footnote 28: "New Philosophy": Bacon's ideas on science and philosophy as set forth in his works.]

[Footnote 29: Royal Society: see note, page 11.]

[Footnote 30: Newton, Sir Isaac (1642-1721): a distinguished natural philosopher of England. Newton was elected a member of the Royal Society in 1672. His most important scientific accomplishment was the establishing of the law of universal gravitation. The story of the fall of the apple was first related by Voltaire to whom it was given by Newton's niece.]

[Footnote 31: "Philosophical Transactions": the publications of the Royal Society.]