1843.] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



417 



THE PHILOSOPHY OF CORAL FORMATIONS, AND THEIR 

 ARCHITECTS. 



No. III. 



The ocean is the mother of earlh, the fruitful womb of production, the 

 tiling principle embodied in forms defined , being the unceasing architect of 

 substance. Generated from the elementary compounds of air and water, 

 living creatures are produced, having peculiar generic character, the mainte- 

 nance of form and quality depending upon climate and association, or, the 

 more uncommon incident, accident of birth. With the change of climate 

 and association, organic bodies undergo a change, genera dividing into or- 

 ders, orders into species; thus the earth multiplies in all its parts, quantities, 

 and qualities, by the action of the living principle manifest in living forms, 

 and in the multitudinous changes continually taking place in the fossil and 

 mineral kingdoms. From the sea weed to the sponge, from the sponge to 

 the lime-secreting polyp, from the polyp to the molluscous animal, from the 

 invisible animalcules to the whale, from the fish to the insect, the bird, and 

 the beast, from the plant to the animal, and from the minutest spark of life 

 to man, the great chain of life is inseparable. 



In the varying strata of the earth, man may see broadly and distinctly 

 marked, epochs of creation — and epochs of destruction — a series of ages 

 succeeding each other — of geneiations succeeding generations — of climates 

 succeeding climates — of local and general changes and catastrophes. Every 

 region of the waters opens to the inquirer new and beautiful truths of na- 

 ture, attests to the forming powers of organic bodies, and speaks of changes 

 to which all species and all individuals are necessarily subject. The coral 

 formation, its varying composition and character, and the sequence of events 

 or manifold changes accompanying it, is as plainly delineated in the chalk, 

 oolitic, and limestone ranges traversing the surface of the earth, as it is in 

 the waters of tropical seas: the one and the other tell the same truthful 

 tale, of myriads upon myriads of bye-gone existences, of fossil animalculae 

 and animals, of species analogous to or identified with those now living 

 within the waters, whose being and existence as fossil or mineral bodies as- 

 sure us of long uninterrupted periods of repose, of sudden and violent catas- 

 trophes, and of causes necessary to effect the end proposed. In the coral 

 rag of the British strata, in the lias and other formations, we find an asso- 

 ciation of species peculiar to warm tranquil seas, their aggregate masses tell of 

 an uninterrupted succession of generations, their sudden extinction, of sudden 

 catastrophes, produced by changes in the position of the earth's surface, and 

 consequently cessation for a time of living action in those regions affected by 

 the change : all distinctly define, by their composition, character, and asso- 

 ciation, the inviolable laws by which oceanic, lacustrine, and terrestrial life is 

 governed in distribution and change. 



Mr. Darwin, treating largely on this subject, observes, " from the limited 

 depths at which reef polypifers can flourish, taking into consideration certain 

 other circumstances, we are compelled to conclude that both in atolls and 

 reefs, the foundation on which the formation was primarily attached, has 

 subsided : and that during this downward movement, the reefs have grown 

 upward." The conclusion he comes to is as weak as is the evidence from 

 whence he has derived it. 



Of the largest lakes disposed within coral groups, such as the Atoll Sua- 

 diva, which is 44 miles long and 34 broad, enclosing a great expanse of 

 water from 250 to 300 feet deep, other and more extensive views may be 

 taken of their mode of formation. We have not yet to learn that the bed of 

 the ocean is full of inequalities, resembling in this respect terrestrial earth : 

 its hill and mountain chains and groups are of great extent, and vary much 

 in their general composition and character ; it has its extensive plains and 

 deep valleys, and its lands favourable or inimical to life: the mountain 

 heights of the earth, represent the bases of the submarine mountains, the 

 one and the other, in the absence of the requisite degree of heat, being in- 

 capable of producing or sustaining life, for even in tropical seas, there are 

 regions in which neither plant nor animal can exist: the filling up of the 

 lower depths must therefore depend upon the matters continually carried 

 into them by currents, or which are precipitated from the waters above 

 them. The lowest region where life is produced, is analogous to the boundary 

 of vegetable existence on the llymalayas or Cordilleras, sustaining species 

 of the simplest organization, wholly devoid of lime and purely siliceous ; the 

 next region is productive of other species, and to this succeeds a region 

 wherein animals secreting calx and other peculiar earths are present in 

 more or less abundance. Mr. Darwin contends, in vain, that ihe polypifers 

 do not build from greater depths than 200 feet ; for although their growth is 

 protracted, and the number of species curtailed within the lower regions, 

 still we are assured that calyx secreting polypifers exist in beds at or near 

 2000 feet in depth, and it is these artificers that lay the foundations and 

 pave the way for the madripora and milleporae, shell fish, erustaceae.&e. that 

 complete the structure. On the bosom of submarine mountains the polypi- 

 fers commence their work, and precluded from descending within deeper 

 and consequently colder regions, they spread themselves upwards, right and 



left, as they are enabled to do from the nature of the soil on which (hey 

 rest: if building on a clump of submarine bills, the valleys can only be 

 filled up by other means, far slower than those of organic action, conse- 

 quently, the structure rises as a great amphitheatre or encircling reef, having 

 openings caused by openings at the foundations, by tidal action, and by 

 local depositions of sand or marl. At other times numerous structures 

 slowly arise independent of each other, or united as so many links in the 

 great chain. The atoll formed, the openings admit the tides, which carry 

 many substances into the lake, and by their rotary motion contribute to 

 prevent the coral from growing within the encircling reef. 



That the inequalities of the ocean bed as well as tidal action give form to 

 the barrier, is demonstrated by the Great C'hagos, which is about 90 nautical 

 miles in lenglh, and 1 in width ; its banks consist principally of rock covered 

 with sand, arranged so as to form a great basin, the central part consisting 

 of a vast plain covered with marl intermingled with shells and marine re- 

 lique ; it slopes outwardly to unfathomable depths : now a circle to this ex- 

 tent cannot for a moment be imputed to vulcanic causes, nor does it appear 

 that it could have been formed otherwise than by being carried round the 

 surface of a vast track of table land, elevated far above the lower plains of 

 the deep. The phenomena of the African and Asiatic deserts give some 

 idea of the mode of formation of atolls. We there find valleys varying in 

 size, surrounded with amphitheatres of hills, the very counterpart of atolls 

 now formed and formtng in the Red Sea. the Indian Ocean, and the Pacific : 

 chains of hills nearly 2000 feet in height and hundreds of miles in length, 

 consisting almost wholly, (from the base to the summit,) of calcareous matter, 

 beds of coral, of shell fish, 8cc, all united in the general mass, strata with 

 strata. Many of these chains of hills are wholly calcareous, and consist of 

 corals and other lime-secreting species ; they are nearly uniform, rising 200 

 or 300 feet in height, above extensive plains of sand, gravel and marl, the 

 amphitheatre having seldom more than 1 or 2 openings leading into the valley, 

 which is generally level with and consists of the same materials as the 

 plains; although there are often several openings ranged at different heights: 

 the soil of the valleys is in fact at all times indentified with the soil of the 

 plains now disposed within the Red Sea, being a greyish marl, (which 

 Darwin very un philosophically terms mud,) combining with vast quantities of 

 shells and other marine exuvias, and some of the valleys have been explored 

 to the depth of more than 150 feet, without meeting with any other material. 

 Again, we have islets and islands formed of peculiar species of shell fish 

 and polypifers, clumps of tubiporae, upwards of 30 feet high and of great 

 width, solid masses of rock formed almost wholly of serpularia, hills of 

 mummullites bounding the Nile, and vast mounds of sea-weed blended with 

 salt and calcareous matter. If, therefore, the reef, the islet, and the atoll 

 sink as they are built up, why have all these vast tracks been elevated ? 

 and why are the many thousand islets and reefs within the Red Sea continu- 

 ally nearing the surface and rising above it? Many of the mountains 

 forming the African chain are also of vast height, and wholly of calcareous 

 formation : none of them present a growth of one continuous family through- 

 out the whole extent, but all demonstrate the vast depth of the calcareous 

 or solid limestone formations : between these mountains and the sea the 

 plains in many places embrace avast area, and while the mountains show 

 that their bases have formerly been washed by the sea, the plains demon- 

 strate their organic origin and end in a fringing reef, which in some place3 

 is wholly removed from the action of the sea, in others, is still laved by the 

 waters, and contains many singular grottos of dead coral, rising from 15 to 

 30 feet from the beach: the beach is of fine shell sand, and gradually shelves 

 into the waters. 



If, as Mr. Darwin would lead his reader to infer, the reef gradually sinks 

 as it is built up, there is nothing to prevent its being uniform to the depth of 

 many thousand feet, but the revealed reefs of chalk, limestone, and oolit- 

 formations of terrestrial earth tell a widely different tale, for even the most 

 solid limestone rock is formed, not of one but, of numerous species, of nume- 

 rous families, of countless individuals, and of the atomic particles of these 

 countless myriads which have undergone decomposition, all of them pos- 

 sessing the same elements, and consequently in their union in the fossil and 

 mineral kingdom, producing the one result, under its several forms of car- 

 bonate and sulphate of lime. Where the reef is built up by living polypi- 

 ters, there the valleys and plains are built up also by broken coral, calcareous 

 depositions and sands ; but, unless aided by tidal contributions, the latter 

 advance towards the surface far more rapidly than the former: aided by 

 tidal action sandbanks form, filling the lower depths, capping submarine 

 mountains, or forming mountains of themselves, as is the case most particu- 

 larly in the Atlantic Ocean. It is to the vast deserts of the earth, virgin is- 

 lands, and fossil formations, existing under every latitude, tint Mr. Darwin 

 has to look for an explanation of coral atolls, islets, islands, and barrier 

 reefs; he says we cannot believe that the broad summits of mountains lie 

 buried at the depth of a few fathoms, and he asks in his simplicity where we 

 can find terrestrial mountain chains many hundred miles in length. A slight 

 glance at the map of the world will answer the latter question, and the very 

 child in navigation will inform htm, that the irregularities of the ocean bed are 



