building corals have continually risen higher and higher, so as to remain in the shallow water, in which alone they can live, and thus in course of ages the condition of things becomes reversed. The once fertile isle disappears beneath the ocean, whereas the coral-reef, rising to just below high-water mark, gradually accumulates shells and sea-weeds; the sea deposits drift of all sorts, and, little by little, a soil is formed which becomes fertile, and presently cocoa-nuts drift from far-away isles, and weeds of many sorts are carried by the birds, or float on the currents, and so the isle becomes fertile—a ring instinct with life, rising perpendicularly from the deep sea on the outer side, and very often on the inner side also.
Where this is the case, and the inner lagoon appears as fathomless as the outer sea, it is supposed that the atoll has been formed on the rim of a sunken crater, colonies of living corals having settled on its surface so soon as it subsided below high-water mark. This theory seems the more probable, from the manner in which you find these circular coral-isles densely clustered in certain localities, and none in other groups, just as in some regions we find innumerable extinct craters covering the whole surface of the land, and can readily imagine that should such a district subside, each cup-like crater might soon be covered with corals.
As in some craters the lava-flow has rent a gap near the summit whereby to escape, and in other craters it has found for itself a subterranean passage, leaving the upper crust unbroken, so in these atolls, some are perfect rings, and the tides ebb and flow within the lagoons by submarine channels, while others have an open passage, deep enough for a ship to sail into the inner lake.
The principal island in the Paumotu group is that of Manga Reva, a cluster of five isles, all within one encircling reef. The main isle is a basaltic mass, rising 2000 feet above the sea-level. It is the most fertile of the group, and is the headquarters of the French bishop and his clergy. The Paumotus have a population of about 5000 persons, the majority of whom are Roman Catholics. They are a fine independent race, and in old days were accounted brave warriors.