CORAL ISLANDS ELEVATED. 465 to the highest point of the Appenines, was raised at one single period from beneath that ocean, in which we know that the limestone of this ridge was formed. Should this have been the case, the absence of the marine alluvium from the higher parts would be accounted for on the same principles which are applied to the denudations of the earth's surface all over the world."* In the above phenomena, we have the association of an active existing cause, with effects that cannot be questioned. We feel the insecurity of the earth on which we stand; for what arose in one earthquake may be consigned by another to the bottom of the ocean. The suddenness or rapidity of the above eruptive agency, may be inferred from the undisturbed state of some of the shells and skeletons; but still more decidedly from the preservation of the animal matter in the ligaments of the bivalves, and from the condition of the fishes of Monte Bolca, as already described in Chap. ii. Book II. The countries most easy of access, which probably contain good examples of volcanic elevation, are the Azores, and the other volcanic islands of the African coast, as well as St. Helena, Ascension, and Owhyhee. Geologists should bear in mind, moreover, "that as all the supra marine land has apparently been elevated by some causes, from the bottom of the sea, there may be marine alluvia beneath terrestrial ones, in many countries which show no traces of a volcanic nature, or of a volcanic origin. It must be remembered, that although the land be supposed to have been elevated from the sea, it by no means follows that this was a single It is much more probable that it was suc event. • Macculloch, Brande's Journal, vol. XIV. pp. 277, 278. cessive, and that the causes operated through a long series of ages."* The coral islands offer proofs of the elevations of submarine strata by expansive forces, acting at periods probably not very remote from our own times; and therefore they are well calculated to throw light on the more ancient and obscure phenomena of the deluge. Nearly all the islands to the south of the equator, between New Holland and the west coast of America, are the productions of polyparies, or, as they are commonly called, of the coral tribe of molluscous insects. But to account for the very considerable heights at which many coral islands stand out of the sea, above whose level these insects cannot build, we must have recourse to an upheaving power; and that power is obviously igneous. We have reason to believe that these organic edifices are founded on the cones of submarine volcanoes. The coral rocks round Tongataboo are ten feet above the high water mark, a terrace which could not be formed by polyparies, or by the deposition of marine exuvia. Interiorly, the island rises in many places 60 or 70 feet higher. In other islands, coral rocks under their most characteristic forms, have been observed, as at Eooa, at altitudes of 300 feet above the sea. Now, it will not surely be inferred that our ocean has sunk 300 feet. Nor need we resort to such an extravagant hypothesis, since the true agent of elevation reveals itself in subjacent volcanoes among these very isles. Toofooa, 70 miles from Tongataboo, exhibits a volcano always burning. Among the Friendly Isles 3 active volcanoes are known. Tafooa, we have already noticed as well as Eap to the eastward of the Carolines, both volcanic, and the latter subject to frequent earthquakes. All the coral reefs shake, when the island Ulea trembles. * Macculloch, Brande's Journal, vol. XIV. pp. 280, 281. VOLCANIC CRATERS OF THE PACIFIC OCEAN. 467 In the inland and elevated parts of Owbyhee coral is observed; an island noted for magnificent volcanic operations. The soil of the adjoining island of Mowee consists of lava and other volcanic matters; along with probably the whole mountain group to which it belongs. To the preceding instances of volcanic action among the coral islands, may be added Tanna, one of the New Hebrides, which contains a very active volcano. Messrs. Forster and Sparrman made an attempt, but unsuccessfully, to reach its burning mountain. The whole of it shook, with projection of ashes, which darkened the atmosphere; and there fell at the same time a rain composed of water, sand, and earth, which might be called a shower of slime. Ambryn in the same group, emitted columns of white smoke, impetuously from a volcanic crater. The Marian Islands are filled with volcanoes. La Perouse describes Assumption Island as covered in every direction with lava torrents. To the north of the Marians, are several groups of small islands, almost all of them volcanic. Many of them indeed, have no other name than Volcano Island; and others have names of similar import, as Sulphur Island. There are two collections of coral reefs, surrounding two of these small islands, to which the imposing title Gardens has been given. Easter Island, to the east of the Society Isles, is arid and volcanic, composed of a porous, light, red lava. From these details it appears quite certain that many of the coral isles, have like Italy been raised out of the ocean by the volcanic intrusion of matter somewhere under their base, or by a general expansive force forming vaults beneath them. It is highly probable that the numerous volcanic chimnies which like Kirauea in Owhyhee rise through the vast Pacific, are remnants of the general convulsion which raged at the deluge, ending in the submersion of some vast primeval continent, corresponding probably in area to the surface of that ocean. But this topic belongs to a subsequent chapter. Having adverted to the coral islands, I shall introduce here such remarks about their influence in modifying the surface of the globe, as may be naturally expected to have a place in a system of geology. The rank which their insect architects hold in the zoological kingdom has been shown in the Table of living and fossil organic genera, p. 457. The great quantity of calcareous polyparies or lithophytes, found alive in the seas of hot countries, and the considerable masses of them met with in the fossil state among our limestone rocks, have caused these animal products to be considered as forming a notable constituent portion of our continents, and as being capable of modifying in an extremely rapid and powerful manner, the submarine surface of our globe. Such views are very common in our modern treatises on Geology. Originally founded on the observations of Captain Cook, and the other early navigators who traversed the south seas, and explored Australasia, they were corroborated in a particular manner by Forster, then by Peron, during his voyage to New Holland in the expedition of Captain Baudin, and afterwards adopted by all natu ralists. It was obvious, indeed, that if the animals which produced these polyparies, designated under the general names of madrepores, or corals, by sailors and even by many geologists, grew as rapidly as those which form the eschars, according to Spallanzani's observations, the stony polyparies ought to produce, in about half a century, or even a much shorter period, by means of the beds they build up to an almost indefinite extent, calcareous masses of prodigious depth and surface. But the first position is more than doubtful, viz., that the astrea, and the caryophylla, are produced with the same rapidity as the eschars; and, it is certain, besides, that these fixed animals cannot live either at great depths, where the solar light and heat exert little or no influence, or so near to the surface of the sea as to be exposed to its violent agitations, far less above that surface. Hence, in the most favourable situations, it is evident that the islands, archipelagoes, and reefs with which the Indian and South Seas are studded, cannot be altogether madreporic, as has been long believed, but merely prominences rising from the bottom analogous to those of the adjoining lands, most commonly volcanic, CONSTRUCTION OF THE CORAL REEFS. 469 which become incrusted with madreporic deposits of greater or less thickness. This is the opinion advanced by MM. Quoy and Gaimard, naturalists of the expedition of Captain Freycinet, who after visiting the same points as Peron, and particularly Timor and the Isle of France, have undertaken to prove in a memoir on the augmentation of lithophyte polyparies considered geologically, that what had formerly been published about the immense erections which the saxigenous polypi are capable of executing, is erroneous and greatly exaggerated. Perhaps these naturalists may have systematised a little too much in the opposite direction. They previously determined that the incrustating polyparies, as the astreæ, the caryophyllæ, and the meandrinæ, are the genera whose faculties of increase appear to be most extensive or least limited. Yet they cannot live at considerable depths, since they have never been met with below a few fathoms from the surface. By their own admission, however, the ramifying polyparies may live at a great depth, and they adduce an instance where at 80 fathoms in south latitude 56°, they obtained by sounding, small branches of living madrepores. It is known, moreover, that in the Mediterranean, even the coral tribe exists at the depth of 1000 or 1200 feet. May not astrea also live far deeper than a few fathoms, though they have not been met with, since there is a great analogy between them, and certain madrepores? Or may it not be supposed that these reefs and islands, based always upon some earthy prominence of a primitive, secondary, or volcanic nature, constituting the bottom of the sea, at first shoot up to a certain height by the aid of numerous branches, of the ramifying polyparies, and are connected and consolidated by the shells which take shelter in their windings; that then the remainder may be formed by beds of astreæ, meandrinæ, and other incrustating polyparies, the action of which will be more lively and rapid as the animals get into more favourable circumstances of heat and light? As to the support which the opinion of Forster and may derive from madrepores being observed on islands at Peron |