CORAL. 



413 



the Madrepore, and has long been erroneously con- 

 sidered as identical with the coral polypus; hence 

 the masses of land alluded to have received the ap- 

 pellation of coral reef's and islands. These have 

 never yet been found in any extent excepting in the 

 Pacific and Asiatic seas, but in these immense 

 waters the coral rocks and reefs are abundant. 



The principal groups of islands of coral forma- 

 tion are, from the New Hebrides, eastward, the 

 Friendly islands, Navigation islands, and the 

 Society islands ; and, to the northward of the lat- 

 ter group, the Marquesas. These groups are separ- 

 ated from each other by channels or seas, wider 

 than those which separate the individual islands 

 which form the respective groups ; but all these 

 waters abound with shoals and minor islets, which 

 indicate the existence of a common base, and show 

 that the processes by which they will hereafter be 

 united above the level of the sea, are in constant 

 operation. 



The structure and progress of these islands to- 

 wards a state of fitness for the habitation of man, 

 has been thus described. At a vast but unknown 

 depth, below the surface of the sea, the insects 

 attach themselves to the upper points and ridges of 

 rocks, which form the bottom of the ocean, and 

 many of which, in the Pacific ocean, are supposed 

 to be of volcanic origin. Upon these foundations, 

 the little architects labour, building up by means of 

 the secretion before described, pile upon pile of 

 their rocky habitations, until at length the work 

 rises above the sea, and is continued to such a 

 height, as to leave it almost dry at low water, when 

 the insect leaves off building upon that part. A 

 solid rocky base being thus formed, sea-shells, frag- 

 ments of coral, and sea-sand, thrown up by each 

 returning tide, and broken and mixed together, by 

 the action of the waves, become in time converted 

 into a sort of stone, and thus raise up the surface 

 higher and higher. The heat of the sun so pene- 

 trates this mass of stone, that it breaks off into 

 flakes, and these flakes are again raised one upon 

 another by the waves, at high water. The ever 

 Active surf continues to throw up the shells of 

 marine animals, and other materials, which fill up 

 the crevices between the stones, and the sand upon 

 the surface being now undistributed, offers to the 

 seeds of trees and plants cast upon it by the waves, 

 a soil upon which they rapidly grow, and over- 

 shadow the dazzling whiteness of the new formed 

 land. Trunks of trees, washed into the sea by the 

 rivers from other countries and islands, find here a 

 resting place, and with these come some small ani- 

 mals, chiefly of the lizard and insect tribes. Even 

 before the trees form a wood, the sea-birds nestle 

 among them, and soon the stray land-bird takes 

 refuge in the bushes. At a latter period, man 

 appears, builds his hut upon the fruitful soil 

 formed by the corruption of the vegetation, and 

 calls himself lord and proprietor of this new crea- 

 tion. 



These islands vary in extent, as well as in the 

 degree of finish to which they have arrived. Of 

 thirty-two examined by captain Beechey, the largest 

 was thirty miles in diameter, and the smallest some- 

 what less than a mile. They were of various 

 shapes, and all formed of living coral, except one, 

 called Henderson's island, which was partially sur- j 

 rounded by it; and they all appeared to be increas- ' 

 ing in size by the active operations of the Zoophytes, 

 which are gradually extending, and building up | 

 above the level of the sea those parts which are i 



at present below the water. Twenty-nine of the 

 number had layoons, (or morasses) in their centres, 

 within which, it has been observed, the smaller 

 species of coral seek a quiet abode, and labour 

 silently and slowly, in throwing up banks, which, 

 in process of time, unite with islets that surround 

 them, and at length fill up the lagoon, so that what 

 was at first a ring of little islands, becomes one con- 

 nected mass of land. All these islands are situated 

 within the action of the trade wind, except one 

 (Oeno,) which is on the verge of it, and follow one 

 general rule in having their windward side higher, 

 and more protected than the other, and not unfre- 

 quently, well wooded, while the other is only a 

 half drowned reef, or wholly under water. At 

 Gambier and Matilda islands this inequality is very 

 conspicuous ; the weather-side of both being wood- 

 ed, and, of the former, inhabited, while the other 

 sides were twenty or thirty feet under water, where 

 they might be perceived equally narrow and well 

 defined. One of these islands (Maiden island,) 

 presented the singular appearance of perpendicular 

 coral cliffs, elevated eighty feet above the level of 

 the sea; these were of dead coral, but the outside 

 of the island was surrounded with a belt of living 

 coral, sloping from the cliffs, to from three to 

 twenty-five fathoms under water, after which it 

 descends abruptly to a depth where a 200-fathom 

 line does not reach the bottom. The surface of 

 this island is flat ; and it is not easy to account for 

 its present elevation, unless by an earthquake or 

 sub-marine volcanic explosion. 



Gambier Group consists of five large islands and 

 several smaller ones, the whole (as well as the five 

 separate islands,) being enclosed in a reef of coral, 

 forming an irregular diamond-shaped space. The 

 older islands are volcanic, and the largest rises in 

 two peaks, 1248 feet above the level of the sea. 

 The outer belt of coral descends abruptly outside 

 to an unfathomable depth, but slopes inward by 

 a decreasing declination, to about 120 or 150 

 fathoms below the surface ; and within this en- 

 closure, a number of low islands are already formed, 

 and others are in progress, rendering it almost cer- 

 tain that, in process of time, the whole space will 

 become one island, each of the original islands being 

 also inclosed with its own reef. These are inha- 

 bited by a race of men with fine Asiatic counten- 

 ances, wearing mustachios and beards, and they ap- 

 peared to be more civilized than those of many other 

 islands. Specimens of spars, crystals, alumine, 

 jasper, and chalcedony, have been procured on 

 these islands by the naturalists who accompanied 

 captain Beechey. They are covered with a deep 

 soil, and well wooded with trees and evergreens of 

 different kinds. 



It is a fact worthy of remark, that on all these 

 islands, a plentiful supply of fresh and sweet water 

 may be obtained, by digging three or four feet into 

 the coral ; and that even within one yard of high 

 water mark, such a supply is to be found. This is 

 an important consideration to the navigators of 

 those seas, where such a resource is so valuable, on 

 account of the extreme heat to which they are ex- 

 posed ; and it shows also the powerful properties 

 of the coral, in divesting the sea-water of its saline 

 particles. These properties, which are probably 

 chemical, and not merely the effect of filtration, 

 have never been examined or experimented upon, 

 but they furnish a subject of consideration for the 

 naturalist, and the man of science. 



Of the rapidity with which the coral grows, we 



