384 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[November, 



Indian Ocean, owe their origin and increase to like causes. The islands of 

 the West Indies and vast barriers on the shores of the main land are coral- 

 line — the Persian Gulf and the whole of the Red Sea are both rapidly filling 

 up, the latter sea being at present barely navigable by vessels of large burthen 

 through a very narrow channel, and by far the greater portion of the main 

 continent of Africa and of Asia, including all the great deserts and mountain 

 chains intersecting them in various directions. Charles T. Bell supposes the 

 advance of land upon the gulf of Persia to be more than 280 miles since the 

 last catastrophe ; and all writers unite with him in supposing that great en- 

 croachments have, and continually are taking place in these latitudes. The 

 clay of the Euphrates contains an excess of sodium, and on either side are 

 immense deserts of sand, salt, bitumen, naphtha, magnesia, soda, and calca- 

 reous matter, while the hill chains dividing them, are wholly composed of 

 matters almost exclusively oceanic. At Cutch and the whole of the northern 

 shores of India, the land has encroached upon the sea to a vast extent; the 

 great Run, 7000 square miles in extent, is one sandy flat containing vast beds 

 ot salt, and the elevated tracks surrounding it demonstrate their origin. The 

 great deserts of Africa, Zaharah, Nubia, Lybia, Egypt, Mesopotamia, and 

 many others, stretching from the Atlantic through Asia, are exclusively 

 oceanic, the entire soil being sands and calcareous matters, beds and hills of 

 salt, chains of hills composed wholly of corals, balani, oysters, and numerous 

 species of shell fish, interspersed with vast accumulations of petrifactions, 

 and the skeleton remains of fishes. Approaching towards Europe the like 

 phenomena have been noticed so far back as the time of Diodorus, Pliny, 

 and Strabo : further proofs of the decrease of the waters are afforded, by the 

 fact of the drying off of large inlaid seas, thus the communication between 

 the Caspian and the Black Sea, the Red Sea and the Mediterranean, have 

 been broken off, and the vast salt lakes of Russia are standing and incontes- 

 tible memorials of the seas retreating therefrom. 



The Red Sea is most abundantly stored with coral formations, lime secre- 

 ting animals, fishes, animalcule and sea treed] i the vast shallows embracing 

 full three-fourths of its entire surface present to the eye of the naturalist 

 the stupendous workings of nature, and the primary causes of many effects 

 manifest in terrestrial earth. Sailing over them during the long continued 

 calms common to this sea, when not a ripple disturbs the surface of the waters, 

 which are bright and blue as the lake of Como, the eye is delighted with 

 the panoramic view beneath. Gardens abounding with animal flowers of 

 every hue, the red pipe coral, green meaudrina, black gorgania, and sponge, 

 purple, blue, yellow, white and brown madrepores and millepores interspersed 

 in clumps and groups with corallines and plants of the most delicate texture. 

 Plains covered with green verdure tenanted by Crustacea, turtles and fishes, 

 valleys covered with a white sand, partially hidden from the view by wings, 

 murices, sea eggs, sea snails, pens, star fish, and scarlet, soldier and 

 hermit crabs— elevated plateaux of pearl oysters— hills of cirrhipedes, and 

 chains of hills of reef coral, whose toweling summits sometimes resemble the 

 roofs of palaces and temples of the richest and most elaborate workmanship, 

 from which pedunculated cirrhi pedes and purple mussels are hanging in clusters, 

 while beneath, wide and magnificent portals open into caves of beautiful coral, 

 where the coral fish resplendent In azure and silver, and green and gold, 

 resort in numbers for their delicate food, cropping the equally gaudy animal 

 flower from its living hud. Above, the sea teams with its living mvriads of 

 phosphorescent anjmalculse, sharks, bonetas, dolphins, black fish, n 

 and numerous other species. 



The calcareous matter covering the valleys and troughs is analogous to the 

 chalk deposits of the earth, consisting of the atomic particles, entire bodies, 

 and portions of bodies ol generation upon generation mixed with the di- 

 gested matter continually deposited by the living. The sands vary in their 

 nature and quantities, in localities being extremely fine, when formed by the 

 death and decomposition of young mollusca, which are thrown up in vast 

 abundance on some of the shores near which they are deposited by tin- pa- 

 rent ; and much coarser when they are produced by the decomposition of 

 murices, oysters, gigantic cockles, and other shell fish having heavy calca- 

 reous shells. The outward reels towards the ocean arc invariably consoli- 

 dated, consisting of the reef coral and various lime-secreting species enve- 

 loped in consolidated rising formation; the reefs always form along the tidal 

 line, and when the rising structure causes the tide to diverge right or left, 

 then, within the disturbed space the zoophytes cease to work, and an opening 

 is left of considerable width and depth, of much advantage to mariners, 

 who are thereby enabled to take refuge within the reefs during stormy wea- 

 ther. This outer reef presents a perpendicular wall to the tidal currents, 

 but generally has a gentle inclination towards shores with two or more pa- 

 rallel chains, thus from Mocha to Yambo there is a continuous reef, and for 

 upwards of 500 miles a tiiple chain of reefs is seen running parallel to the 

 coast, and to the mountain chains of Arabia bordering the sea. The inner 

 reefs are variably composed, their elevated parts being generally or the like 

 conformation of the outer wall, but the interior is sometimes filled by coral 

 banks heaped up by storms, consisting of broken coral sands and weeds; 

 upon these, in the long continued calms common to this sea, vast multitudes 

 of mollusca resort, which are buried in the next periodical disturbance, thus 



stratum upon stratum is formed, until the bank tops the water, sometimes 

 cutting off vast tracks from the main ocean, which, when perfectly isolated, 

 soon become a portion of the desert. The reef is sometimes formed by the 

 united labours of numerous species of lime-secreting animals, separately 

 working in groups and families, or confusedly blending together and em- 

 bracing each other in the general ruin, the coral polyps enveloping all the 

 crustace;e and corallines, and the relics of the dead in their stony folds. 

 Many entire hills are formed by particular families, such as serpula contor- 

 tuplicata, balani, and white tube coral, and others are wholly formed of cal- 

 careous matters or sea weed, the whole united mass being one vast receptacle 

 of the dead, and so long as covered by the waters, one general birth place of 

 the living: the like phenomena of coral formations is common to all tro- 

 pical seas. 



Mr. Dalrymple, who first drew attention to this important subject, observes, 

 that in the eastern seas, coral banks grow by a quick progression towards the 

 surface ; but the winds heaping up the coral from deeper water, chiefly acce- 

 lerate their formation into shoals and islands. They become gradually shal- 

 lower ; and when once the sea meets with resistance, the coral is quickly 

 thrown up by the force of the power breaking against the bank ; and hence 

 it is that in the open sea, there is scarce an instance of a coral bank having 

 so little water, that a large ship cannot pass over it, but it is also so shallow 

 that a ship would ground on it. The coral banks were observed by him in 

 all stages of growth, some in deep water, others with few rocks appearing 

 above the surface, some just formed into islands, and others covered with 

 land vegetation. Bars of sand and coral also form, cutting oil large portions 

 of the waters, the isolated portion being soon filled up by this material. The 

 violence of the waves, he observes, gives the direction and form to the reefs, 

 which are long and narrow ; but [when .not exposed to the common monsoon 

 they assume irregular forms, according to the accident of circumstances. 

 Such in truth is the origin of many coral banks ; but this mode of formation 

 cannot apply to those barrier reels and rock built islands which constitute 

 the by far greater portion of coral formations. It is true that all reefs re- 

 ceive increase by continued sedimentary depositions; but many of the inner 

 reefs of seas being beyond the action of the storms, are entirely built up by 

 the living architects, without the aid of broken coral and sands from deeper 

 waters : thus all navigators speak of these enormous barriers and local ac- 

 cumulations as presenting seaward a solid wall of limestone of unfathomable 

 depth, and such could not be the case were they built up by the sands and 

 broken coral alone. 



Ihc analogous formations intersecting the earth in hill and mountain 

 chains of limestone, oolite and chalk, give correct ideas of the disposition and 

 shape of these reefs now forming within tropical seas ; the limestone has in- 

 variably one or more perpendicular faces, the same inclination pervading the 

 reef, the extreme height not exceeding 4000 feet: the chalk having also oc- 

 casionally one abrupt face, but being in many instances dome shaped ; the 

 larger formations generally running for a considerable distance in a direct 

 line, the smaller being grouped together, being as evidenced by their organic 

 remains formed in the shallows of warm and tranquil seas. 



1 he Red Sea, as previously observed, is literally choked up w ith coral reefs, 

 sands, and embankments, composed of broken corals, shell fish, Ike. ; and the 

 lower depths are also rapidly filling up with the finer decomposed particles 

 of lime secreting animals, fuci and other organic remains ; since the days of 

 the Pharoahs, thousands of square miles have been abstracted from this sea, 

 from the Persian Gulf, and hundreds of islands have reared their crests far 

 above the surface of the waters. Sea port towns once accessible to vessels of 

 heavy burthen, are now lost in the distant desert plain, or are inapproachable 

 for miles. Ehrenberg tells us that the ancient harbours are filled up 

 with the debris washed into them by storms, but this is not the fact ; the 

 present sue of Yambo is on a recent coral reef,- from which the inhabitants 

 say the waters are continually receding. Djeddah is inapproachable by our 

 vessels for two or three miles, the solid coral limestone rock approaching in 

 all parts of this intervening space to the very surface of the waters, and 

 Lohheih, the great coffee mart, once a well frequented port, is inapproachable 

 for full five miles ; the coast on the Arabian side is bounded by continuous 

 reefs of recent coral, now standing from 20 to 00 feet above high water mark 

 and chains of lakes are formed both by this general decrease of the waters, 

 and also by accumulating sand banks. Beds of pearl oysters, and hills of 

 peculiar species of lime-secreting animals common to this sea, may be found 

 many miles inland. The accumulations of coral, sand, and calcareous matter 

 are of Incredible extent and thickness, embracing many thousand square 

 miles between the sea and the hills of Arabia and Africa. Few of the is- 

 lands are or can be inhabited, being desert soil, wholly devoid of vegetation, 

 with the exception of the amphibious mangrove, and a few stunted shrubs 

 and coarse grasses, and such plants that love a barren acrid soil : they arc 

 the resort of pelicans and other sea birds, whose dung sometimes covers the 

 surlace to a considerable extent. In consequence of the want of rain, these 

 islands continue bare and desolate from generation to generation. 



The phenomena of coral reefs similate in a 1 parts of the ocean where they 

 are produced, but the after changes which take place on their surface depend 



