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THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[December, 



analagous to those of terrestrial earth, that they form hill and mountain 

 chains and clumps, and consequently valleys and extensive plains : there is 

 no reason required why their summits do not appear above the waters, the 

 sandbank and the hidden rock are quite sufficient proof that they are there. 

 The fishers of the Mediterranean tell us that coral is found, even in those 

 latitudes, growing at the depth of 900 feet ; therefore, if heat necessary to its 

 existence, propagation and increase, is here manifest, how much deeper have 

 we a right to expect it in tropical seas. Were the great barrier reefs and 

 atolls uniform in their growth and material, from their bases to the surface 

 of the waters, and was this sinking strikingly manifest in all coral regions, 

 then might we embrace Mr. Darwin's hypothesis; but wdien we find the 

 whole earth we inhabit intersected and covered with like formations, we are 

 naturally led to conclude that nature perfects her works without violence : 

 he very candidly tells us that he cannot furnish, nor are we to expect proofs 

 of continued subsidence, and so says Mr. Lyell, when he talks of elevatory 

 forces in action. 



The poly pifers build in regions adapted to their nature; and bearing in 

 mind that lime-secreting animals cannot exist without heat, if, perchance, 

 they do without light, which I much question, we must conclude that Malte 

 Brun is in error when he asserts that light only extends 270 feet in depth, 

 and that heat extends but a little farther. The temperature of the ocean 

 diminishes as we descend, much in the same manner as it decreases as we 

 ascend elevated portions of the earth ; and the same laws of nature which 

 regulate the distribution, habits, and characters of species, are applicable to 

 both. It matters little to the philosopher whether the coral reef, islet, or 

 islands, or the vast amphitheatre existing wilhin tropical seas (unwisely 

 termed atolls) are built by one or by 1000 species of polypifers, we feel assured 

 that they are built, that they rise unequally, that they continue to increase, 

 that in composition and character, in form and disposition, they resemble the 

 calcareous formations of the earth now far removed from the ocean, as is 

 demonstrated by the vast regions of Africa and Asia ; and that they are con- 

 tinually adding to the earth. Upon examination we find certain species of 

 hardy madrepores rising to the level of the tide, and bidding the breakers 

 defiance ; that almost invariably they replace some species and give place 

 to others ; that at nearly the greatest depths sounded, some of these 

 lime-secreting species are found ; and that every region, beneath every lati- 

 tude, has its peculiar vegetation, or peculiar animal species. The polypifers, 

 checked in their growth by currents and depositions of sands, build laterally, 

 towards the surface of the waters, to the right and to the left. Jn the shal- 

 lows of the Red Sea there are numerous circular reefs formed exclusively by 

 one particular reef species throwing their branches out on every side; in the 

 valley between these reefs, formed by clusters of such reefs, we see a variety 

 of species in solitary clumps, or intermingling with each other, and appa- 

 rently struggling for existence ; but however circular the reef may appear 

 above the waters, this peculiar form soon ceases beneath, for on that side of 

 it not allected by the currents, and in very quiet parts within the barrier or 

 mcircling reefs, the growth of the coral is nearly uniform, and the spaces 

 between each group becoming rapidly filled with living coral, the crowning 

 islets always preserve their tabular appearance: thus, when they have 

 spread to a vast extent, they sometimes become partially or wholly destroyed 

 by sudden involutions of sand thrown upon them by tempests, and the whole 

 family is thereby destroyed. In general they dip with a gentle inclination 

 into deeper waters, and sometimes they exhibit epochs of general destruction, 

 whole fields having been suddenly destroyed, from which, in the course of 

 time, fields of lesser extent again spring up, to be destroyed in turn: thus 

 many of the vast atolls or islands dip by a succession of steps or ledges into 

 the ocean depths : the barrier, encircling, and fringing reefs, always present 

 one or more precipitous sides, varying from a few inches to some hundreds 

 of feet in thickness. 



Ehrenberg, whose authority appears to stand high with some people, has 

 made many unwarrantable assertions regarding the phenomena of the Red 

 Sea, of which, from his very slight acquaintance with it, he could know, and 

 evidently does know, little or nothing. He states that the corals only coat 

 other rocks in a layer from one to two feet in thickness, or at most to a 

 fathom and a half ; there are thousands of elevated islets in this sea. and 

 vast tracks flinging its shores, prove the direct negative to this assertion. 

 I have seen many families of tubiporse standing above high water mark full 

 30 feet in height and many yards in diameter on every side, and there is 

 every reason to believe that their bases, several fathoms beneath the waters, 

 are of the like composition. He speaks of massive corals which he imagines 

 to be of such vast antiquity that they might have been beheld by Pharoah — 

 these are large clumps of meandrina, the growth of from 30 to 50 years ; he 

 tells us harbours fill. up with sediment, sand, and shell, proving thereby that 

 he had never visited the principal ports; 1 believe that his visits were con- 

 fined to Massouah. It is true, in calculating the growth of coral, latitude, 

 dip, and inclination, must be taken into account, and also the many destroy- 

 ing or retarding causes of increase of the calcareous mass, for like the grass 

 of a meadow, the gelatinous or living portion is liable to be continually 

 cropped by the coral and other fishes, which continually feed upon them. 



The experiment of Dr. Allen, of Forres, as related by Darwin, who, having 

 20 species of living coral of 10 lb. weight each, found that after seven months 

 they had become immoveably fixed, and many feet in length, stretching in 

 the directi n of the parent reef, is a demonstrable proof of the rapid growth 

 of many species of reef coral ; again, the relation of Lieut, Welstead, in 

 which he says, that a ship in the Persian Gulph had her copper bottom in- 

 crnsted, in the course of 20 months, with a layer of coral two feet in thick, 

 ness, which it required great force to remove ; also, the incrustation of 

 anchors and other substances exposed for a short time in deep waters, are 

 further confirmation of the rapid growth of coral tinder favourable circum- 

 stances. Captain Moresby speaks of knolls, in the Maldiva amphitheatre, of 

 not less than 100 yards in diameter, and 250 feet to 300 feet deep, and in the 

 shallows of the Red Sea these knolls are beyond number, consisting of 

 branching madrepoiae of one particular family, growing up like one huge 

 pillar, with branches radiating from every side, and festooning from the 

 summit, knoll with knoll, until they fairly entwine with each other; the 

 general structure has been formed by the successive growth and death of 

 individuals, or from the base of the trunk and lower branches, madrepore or 

 millepore having consolidated. It is not from the branches being accidentally 

 broken off that the reefs receive increase, but principally, from the general 

 struggle for existence of species with species; thus, if the red coral attain the 

 height of three feet in 10 or 15 years, other species springing up immediately 

 around its base, enclose it within their stony folds, and they, in turn, be- 

 come buried beneath rising generations : thus the millepora in the Pacific 

 encroach upon the porites and millepora complanata, and the latter upon 

 the strongly branched madrepora. Matilda atoll, described by the crew of a 

 wrecked whaling vessel as "a reef of rocks," was, when Captain Beechcy 

 visited it 34 years afterwards, a lagoon island fourteen miles in length, ami 

 having one of its sides covered with high trees ; and although, from disturb- 

 ing causes, some of the islets and islands of the Red Sea do not exhibit a 

 sensible increase during a long interval of time, the native duellers on the 

 coasts relate m.iny remarkable instances of addition to the main land, and 

 to islands which they resort to for the purpose of fishing for pearl, and tor- 

 toise-shell. 



As the tidal action gives the direction to the outside of the barrier, so 

 does it very often, by being introduced therein, give form to the interior of 

 the reef, the hollow or central basin, resulting from accident, being preserved 

 from filling up by the tides, and by constant depositions, which prove fatal to 

 the polypifers, and prevent their extending over the basin. It is well known 

 that almost all the large lagoons communicate with the ocean by one or 

 more openings, and by these passages the waters bring in quantities of sand 

 and marl, which constitute in varying proportions the bottom of these la- 

 goons ; but if the encircling reef prevent the intrusion of these matters, the 

 lagoon is soon filled up with living coral and shell fish. The larger atolls, as 

 they are termed, are, more properly speaking, vast amphitheatres, some- 

 times formed of harrier coral, at other times of sand banks, calcareous mat- 

 ters, and dead coral or limestone rock ; the interior being very rugged and 

 unequal, numerous islets appearing above or beneath the surface, sometimes 

 united at their base, forming groups and chains of hills, at other times running 

 along the shores of the main land, as though marking out its future boun- 

 dary in that quarter : the circular form of these reefs is a necessary conse- 

 quence of their continued increase ; for having fixed itself in the ocean bed 

 without reference to the nature of the bed, the polypifers radiate on every 

 side, as well as upwards, consequently, if no disturbing causes interfere, 

 its assumption of the circular form is certain: such indeed is the mode of 

 growth of astire, meandrina, and other clump-like corals, the branchilorm 

 differing in giant growth alone : but there is no law commanding this form, 

 for many clumps are square, oblong, or irregular : in fact, these stupendous 

 edifices are produced by very feeble and minute creatures, of the lowest or- 

 ganization, powerless, and depending upon favourable circumstances of lati- 

 tude, dip, and inclination, for their existence and propagation, and whether 

 they extend laterally, or around the level surlace of a submarine mountain, 

 or from clumps of rock, or sand, depends upon the chance of circumstances 

 more than upon design. Many of the lagoons open down into the valleys of 

 the deep, others are formed from the multiplied depredations of coral fish, 

 adapted by the thick scaly coats, to glide through the coral branches with 

 impunity, like the more delicate corals living within the encircling 

 reefs, feeding upon the latter, and thus retarding their growth, permitting 

 only the more hardy and quicker growing madrepores to build up their pe- 

 culiar edifices until they reach the surlace of the waters. 



Mr. Darwin speaks of the limited depth at which reef building polypifers 

 can llourish, at the same time he quotes Captain Beechey, who informs us- 

 that off Keeling atoll all the soundings, even the deepest, were on coral, and 

 what I have previously slated is quite sufficient to prove that according to 

 the laws of light and heat, which regulate their existence, composition, and 

 character, they must exist in much greater depths than in the Mediterranean. 

 -•Egean or Adriatic seas. Most of the atolls in the low Archipelago ate of 

 an elongated form; thus, Bow Island, which is 30 miles broad, is not more 

 than 5 miles w ide ; numerous other islets and atolls bear the like proportions. 



