The great Chagos Bank, whose structure and dead coral-trunks have been thoroughly investigated by Captains Moresby and Powell, is the more interesting to us, because we may regard it as a prolongation of the more northern Laccadive and Maldive Islands. I have previously directed attention in another work[KU] to the importance of the order of succession of the Atolls, which are exactly in the direction of a meridian as far as 7° south lat., in reference to the general mountain system, and the form of the earth’s surface, in Central Asia. The meridian-chains, which mark the intersection of many mountain-systems running from east to west at the great bend of the Thibetian river Tzang-bo, correspond with the great meridian mountain rampart of the Ghauts and of the more northern Bolor in further or trans-Gangetic India. Here lie the parallel chains of Cochin China, Siam, and Malacca, as well as those of Ava and Arracan, which, after courses of unequal length, all terminate in the gulfs of Siam, Martaban, and Bengal. The bay of Bengal appears like an arrested effort of nature to produce an inland sea. A deep inbreak of the waters, between the simple western system of the Ghauts, and the very complex eastern trans-Gangetic system, has swallowed up a great part of the eastern lowlands, but met with an impediment not so easily overcome in the early existing and extensive table-land of Mysore. An oceanic inbreak of this nature has given rise to two almost pyramidal peninsulas of very different length and narrowness; and the prolongation of two opposing meridian systems, the mountain system of Malacca in the east, and the Ghauts of Malabar in the west, manifests itself in submarine, symmetrical series of islands, on the one side in the Andaman and Nicobar Islands, which are poor in corals, and on the other in three long-extended archipelagos of Atolls—the Laccadives, the Maldives, and Chagos. The last, called by mariners the Chagos Bank, forms a lagoon, belted by a narrow, and already much broken coral-reef. The length of this lagoon is 88, and its breadth 72 miles. Whilst the enclosed lagoon is only from 17 to 40 fathoms deep, bottom was scarcely found at a depth of 210 fathoms at a small distance from the outer margin of the coral wall, which appears to be now sinking.[KV] At the coral-lagoon, known as Keeling-Atoll, south of Sumatra, Captain Fitz-Roy states, that at only 2000 yards from the reef, no soundings were found with 7200 feet of line.