414 



MUSEUM OF ANIMATED NATURE. 



[Phytozoa, 



Sometimes reefs rather fringe than encircle islands ; 

 and soraetimfs vast reefs form barriers running for 

 milfs parallel to a coast. Such is the great barrier 

 descril)ed by Flinders as fronting the north-east coast 

 of Australia, having a length of nearly a thousand 

 miles : it runs parallel to the shore, at a distance of 

 twenty, thirty, and in some fifty and even seventy 

 miles; and the arm of the sea between it and the 

 shore varies from ten to twenty fathoms in depth, 

 this increasing at one end to forty and even 

 sixty. In reference to Keeling Island, Mr. Darwin 

 writes, " I am glad we have visited these islands; 

 such formations surely rank high amongst the won- 

 dcrful objects of this world. It is not a wonder 

 which first strikes the eye of the body, but rather, 

 after reflection, the eye of reason. We feel sur- 

 prised when travellers relate accounts of the extent 

 of certain ancient ruins ; but how utterly insignifi- 

 cant are the greatest of these when compared to 

 the pile of stone here accumulated by the work of 

 various minute animals ! Throughout the whole group 

 of islands every single atom (excluding oarlh sub- 

 sequently brought in vessels from Malacca and 

 Java\ even from the smallest particle to large frag- 

 ments of rock, bears the stamp of having been sub- 

 jected to the power of organic arrangement. Captain 

 Fitzroy, at the distance of little more than a mile 

 from the shore, sounded with a line 7200 feet long, 

 and found no bottom. This island is therefore a 

 lofty submarine mountain, which has a greater in- 

 clination than even those of volcanic oiigin on the 

 land." Now as the laraelliform coral polypes, to the 

 untiring labours of which these islands, circular 

 reefs, and vast barriers are due, cannot exist at a 

 great depth, and indeed on the contrary, as was 

 proved by Mr. Darwin, cease to exist at a short dis- 

 tance below ten fathoms, and prefer a less depth, 

 where they feel the influence of the light and 

 vrarmth of the sun, it becomes a question under 

 what circumstances these vast masses, these reefs, 

 these belts, these islands, have been deposited, and 

 which are incontestably coral in their structure. 



" As long," says Mr. Darwin, " as no facts beyond 

 those relating to the structure of lagoon islands were 

 known, so as to establish some more comprehensive 

 theory, the belief that corals constructed their habi- 

 tations, or, speaking more correctly, their skeletons, 

 on the circular crests of submarine craters, was both 

 ingenious and very plausible. Yet the sinuous 

 margin of some, as in the Radack Islands of Kot- 

 zebue, one of which is fil'ty-two miles long by twenty 

 broad, and the narrowness of others, as in Bow 

 Island (of which there is a chart on a large scale, 

 forming part of the admirable labours of Captain 

 Bcechey), must have startled every one who con- 

 sidered this subject." Indeed, where reefs encircle 

 islands, as in the case of Tahiti, we cannot suppose 

 them based on the sides of a crater ; and in the in- 

 stance of lagoon islands, on the volcanic theory, we 

 ought to find the lagoon of tremendous depth. We 

 consider that the tiieory of subsidence renders the 

 whole operation clear, and here we must quote the 

 words of Mr. Darwin, whose admirable elucidation 

 of this subject we earnestly recommend to the atten- 

 tion of our readers. " The theory is simply, that as 

 the land with the attached reefs subsides very gra- 

 dually, from the action of subterranean causes, the 

 coral-building polypi soon raise again their solid 

 masses to the level of the water; but not so with 

 the land — each inch lost is irreclaimably gone ; as 

 the whole gradually sinks, the water gains foot by 

 foot on the shore, till the last and highest peak is 

 finally submerged. 



"Before I explain this view more in detail, I 

 must enter on a few considerations which render 

 such changes of level not improbable. Indeed the 

 simple fact of a large portion of the continent of 

 South America still rising under our eyes, and 

 abounding with proofs of similar elevations on a 

 grander scale during the recent period, takes away 

 any excessive improbability of a movement similar 

 in kind, but in an opposite direction. Mr. Lyell, 

 who fii-st suggested the idea of a general subsidence 

 with rfcference to coral reefs, has remarked that the 

 existence of so small a portion of land in the Pacific, 

 where so many causes, both aqueous and igneous, 

 tend to its production, renders such sinking of the 

 foundation probable. There is, however, another 

 argument of much greater weight, which may be 

 inferred from the inconsiderable depth at which 

 corals grow. We see large extents of ocean, of more 

 than a thousand miles in one direction, and several 

 hundred in another, scattered over with islands, none 

 of which rise to a greater height than that to which 

 waves can throw fragments or the wind heap up 

 sand. Now, if we leave out of the question subsi- 

 dence, the foundation on which these reefs are built 

 must in every case come to the surface, within that 

 small limit (we may say twenty fathoms) at which 

 corals can live. Ihis conclusion is so extremely 

 improbable, that it may at once be rejected ; for in 

 what country can there be found a broad and grand 

 range of mountains of the same height within one 



hundred and twenty feet ? But on the idea of sub- 

 sidence the case is at once clear. As each point, 

 one after another, according to its altitude, was sub- 

 merged, the coral grew upwards, and formed the 

 many islets now standing at one level. 



"Having endeavoured on general grounds not 

 only to remove any extreme degree of improbability 

 in the belief of a general subsidence, but likewise to 

 show that it is almost necessary to account for the 

 existence of a vast number of reefs on one level, we 

 will see how far the same idea will apply to the 

 peculiar configuration in the several classes. Let 

 us imagine an island merely fringed by reefs extend- 

 ing to a short distance from the shore ; in which 

 case, as we have before remarked, there is no diffi- 

 culty in understanding their structure. Now, let 

 this island subside by a series of movements of ex- 

 treme slowness, the coral at each interval growing 

 up to the surface. Without the aid of sections it is 

 not easy to follow out the result; but a little re- 

 flection will show that a reef encircling the shore at 

 a greater or less distance, according to the amount 

 of subsidence, would be produced. If we suppose 

 the sinking to continue, the encircled island must, 

 by the submergence of the central land, but upward 

 growth of the ring of coral, be converted into a 

 lagoon island. If we take a section of some encir- 

 cled island on a true scale, as for instance. Gambler, 

 which has been so well described by Captain 

 Beechey, we shall not find the amount of movement 

 very great which would necessarily change a well- 

 characterised encircling reef into as characteristic a 

 lagoon island. 



" It may be said, granting the theory of subsi- 

 dence, a mere circular disc of coral would be formed, 

 and not a cup-shaped mass. In the first place, even 

 in reefs closely fringing the land, the corals do not 

 grow on the shore itself, but leave a shallow chan- 

 nel ; secondly, the strong and vigorous species, which 

 alone build a solid reef, are never found within the 

 lagoon, they only flourish amidst the foam of the 

 never-tiring breakers. Nevertheless, the more deli- 

 cate corals, though checked by several causes, such 

 as strong tides and deposits of sand, do constantly 

 tend to fill up the lagoon ; but the process must be- 

 come slower and slower, as the water in the shallow 

 expanse is rendered subject to accidental impurities. 

 A curious instance of this happened at Keeling 

 Island, where a heavy tropical storm of rain killed 

 nearly all the fish. When the coral at last has filled 

 up the lagoon tothe height of lowest water at spring- 

 tides, which is the extreme limit possible, how after- 

 wards is the work to be completed ? There is no 

 high land whence sediment can he poured down ; and 

 the dark blue colour of the ocean bespeaks its purity. 

 The wind carrying calcareous dust from the outer 

 coast is the only agent which can finally convert 

 the lagoon island into solid land, and how slow must 

 this process be ! " 



With respect to an enormous reef skirting a con- 

 tinent, it is easy to conceive how a depression of the 

 shores of that continent, continued slowly, will give 

 rise to an elevated mass of coral, the myriads of 

 beings working upwards, to maintain the proper 

 degree of depth, while the channel between the 

 reef and the coast will be gradually made ft'ider 

 and deeper. In this way may we account for the 

 formation of the vast coral-bank skirting the north- 

 east of Australia, and running parallel to the coast. 



We have not room to follow Mr. Darwin through 

 all his arguments or enter into all his observations; 

 sufiice it to say that the very facts adduced to prove 

 elevation often prove the contrary, though at the same 

 time it must be conceded that many lagoon islands, 

 originally the result of subsidence, may have again 

 been more or less elevated, and that in latitudes 

 where subterranean forces are active, alternate, and 

 irregular, movements of subsidence and elevation 

 are quite to be expected; especially when "the 

 space lies directly between the well-marked area 

 of elevation and the enormous one of subsidence." 

 Moreover, there are coral reefs which show no 

 trace of subsidence, but prove a recent elevation 

 of the bed of the sea, on which the coral polypes 

 have established themselves, where the shallow 

 depth of the water favoured their operations. Mr. 

 Darwin sums up his interesting observations as 

 i'ollovvs : " In the first place reel's are formed around 

 islands or on the coast of the mainland, at that 

 limited depth at which the efficient classes of Zoo- 

 phytes can live ; and where the sea is shallow, 

 irregular patches may likewise be produced ; after- 

 wards, from the effects of a series of smaller sub- 

 sidences, encircling reefs, grand barriers, or lagoon 

 islands are mere modifications of one necessary result. 

 Secondly, it can be shown on the above views, 

 that the intertropical ocean throughout more than 

 a Iiemisphere mny be divided into linear and pa- 

 rallel bands, of w Inch the alternate ones have under- 

 gone within a recent period the opposite movements 

 of elevation and subsidence, riiirdly, that the 

 points of eniption seem invariably to fall within 

 areas subject to a propulsion from below. The 



traveller who is an eye-witness of some great and 

 overwhelming earthquake, at one moment of time 

 loses all former associations of the laud being the 

 type of solidity! so will the geologist, if he believe 

 in these oscillations of level (the deeply seated 

 origin of which is betrayed by their forms and vast 

 dimensions), perhaps be more deeply impressed 

 with the never-ceasing mutability of the crust of 

 this our world." Such then are the labours of the 

 coral polypes. 



" Unconiclouf, not unworthy Instruments, 

 By which s hmnd invisible was rearing 

 A new crpstion in the secret deep. 

 Omnipotence wroii|;>it in them, with them, by tham ; 

 Hence what Omnipotence stone could do 

 Worms did. 1 saw the living pile ascend 

 The mausoleum of its architects, 

 Still dying upwards as their Isl>oura closed, 

 ^lime the material, but the slime was turned 

 To adamant by their petriHc touch. 

 Frail were their frames, ephemeral their lives ; 

 Their masonry imperishable." MoNioontBT. 



Many coral polypes are acrid, and have the pro- 

 perty of stinging. Such are noticed by M. Quoy: 

 and Mr. Darwin found two species of Millepora 

 which had this power when taken fresh from the 

 water, and he says, that on merely touching his face 

 with a branch, on one occasion he felt sharp and 

 instantaneous pain. The same writer observed 

 two species of fish (sparus) which exclusively feed 

 on coral : both are of a splendid bluish green, but 

 one invariably lives in the lagoon, the other in the 

 outer breakere. Mr. Liesk assured him that he had 

 seen repeatedly whole shoals of these fish grazing 

 with their strong bony jaws on the tops of the coral 

 branches. It has been sometimes thought that 

 coral-eating fish were poisonous, but such was not 

 the case with the spari m question. 



Let us now turn to the corticiferous Polypifera, 

 a group of which the red coral of commerce may 

 be taken as a type. Ramified and arborescent 

 from a fixed base, these Polvpiaria present us with 

 an external living fleshy envelope, bearing and con- 

 taining polypes, and an internal firm inorganic 

 axis or Iramework, calcareous or horny, or both in 

 alternate joints. There are no cells or tubes in the 

 axis or skeleton, but polype cells are scattered over 

 the living fleshy envelope, into which the polypes 

 can retire. 



The red coral of commerce (Corallium rubrum). 

 Fig. .3836, is found in the Mediterranean and the 

 Red Sea. It grows arborescent, attached to stones, 

 rocks, fragments of lava, and various hard substances 

 at the bottom of the water. Its axis is of a beauti- 

 ful red, and of sufficient hardness and closeness of 

 texture to take a fine ^lolish. In its natural state it 

 is covered with a whitish rind, united to the axis 

 by a reticulated membrane abounding with milky 

 follicles ; on the surface of the fleshy rind are thinly 

 scattered tubercles with a cavity or cell in which a 

 milk-white and almost transparent polype is lodged, 

 having the mouth surrounded by eight conical 

 tentacles. This fleshy rind becomes friable and 

 chalky when dried. 



Unlike the Madrepores, Red coral is of slow 

 growth, and at a moderate depth requires eight or 

 ten yeai-s to grow to the height of a foot, which it 

 seldom surpasses. When full grown it increases 

 slowly in circumference, and the living rind dies 

 at length, leaving its axis to the attacks of various 

 minute boring animals, which soon pierce it in all 

 directions and cause its destruction. 



The depth at which coral grows varies from 

 six or seven fathoms to sixty or a hundred; 

 seldom much deeper: it is said to prefer along 

 the French coast the surface of rocks inclining 

 to the south, and in the Straits of Messina those 

 with an eastern aspect. In these straits, where 

 the heat of the sun penetrates very deeply info the 

 water, the coral is found even below a hundred 

 fathoms, but of inferior quality. It would appear 

 indeed that its ratio both of growth and quality 

 depends upon the depth (and consequent influence 

 of light and warmth) at which it exists; and the 

 most beautiful is that obtained in shallow water, 

 permeated as it were by the rays of the sun. To 

 acquire a determinate height, say one foot, coral 

 requires eight years in water varying from five to 

 ten fathoms, ten years in water from ten to fifteen 

 fathoms, and from twenty-five to thirty years in 

 water of the depth of a hundred fathoms. It is said 

 that fifteen varieties of coral are distinguished in 

 commerce according to their degrees of hardness 

 and brilliancy of colour: that procured off' the coast 

 of France is in the highest esteem, as is that also 

 from the Italian seas. On the African shores of the 

 Mediterranean the colour is less brilliant, and 

 though the branches are thicker,, their texture is 

 less compact. 



Coral fisheries are established in many paits of 

 the Mediterranean. It would appear that the ground 

 is divided into separate portions, one of which is 

 dragged only once every ten years, in order to allow 

 of the growth of a fresh crop of coral. The appara- 

 tus for dragging it is very rude, and consists of a 



