THIS DREADFUL SIGHT was the first of a whole series of maritime catastrophes that the Nautilus would encounter on its run. When it plied more heavily traveled seas, we often saw wrecked hulls rotting in midwater, and farther down, cannons, shells, anchors, chains, and a thousand other iron objects rusting away. Meanwhile, continuously swept along by the Nautilus, where we lived in near isolation, we raised the Tuamotu Islands on December 11, that old “dangerous group” associated with the French global navigator Commander Bougainville; it stretches from Ducie Island to Lazareff Island over an area of 500 leagues from the east-southeast to the west-northwest, between latitude 13 degrees 30′ and 23 degrees 50′ south, and between longitude 125 degrees 30′ and 151 degrees 30′ west. This island group covers a surface area of 370 square leagues, and it’s made up of some sixty subgroups, among which we noted the Gambier group, which is a French protectorate. These islands are coral formations. Thanks to the work of polyps, a slow but steady upheaval will someday connect these islands to each other. Later on, this new island will be fused to its neighboring island groups, and a fifth continent will stretch from New Zealand and New Caledonia as far as the Marquesas Islands. The day I expounded this theory to Captain Nemo, he answered me coldly: “The earth doesn’t need new continents, but new men!” Sailors’ luck led the Nautilus straight to Reao Island, one of the most unusual in this group, which was discovered in 1822 by Captain Bell aboard the Minerva. So I was able to study the madreporic process that has created the islands in this ocean. Madrepores, which one must guard against confusing with precious coral, clothe their tissue in a limestone crust, and their variations in structure have led my famous mentor Professor Milne-Edwards to classify them into five divisions. The tiny microscopic animals that secrete this polypary live by the billions in the depths of their cells. Their limestone deposits build up into rocks, reefs, islets, islands. In some places, they form atolls, a circular ring surrounding a lagoon or small inner lake that gaps place in contact with the sea. Elsewhere, they take the shape of barrier reefs, such as those that exist along the coasts of New Caledonia and several of the Tuamotu Islands. In still other localities, such as Réunion Island and the island of Mauritius, they build fringing reefs, high, straight walls next to which the ocean’s depth is considerable.