On a coral reef you are treading on rock that the reef-building polypifers of ages have left behind them as evidences of their idle and apparently useless lives. You might fancy that the reef is formed of dead rock, but it is not: that is where the wonder of the thing comes in—a coral reef is half alive. If it were not, it would not resist the action of the sea ten years. The live part of the reef is just where the breakers come in and beyond. The gelatinous rock-building polypifers die almost at once, if exposed to the sun or if left uncovered by water.

Sometimes, at very low tide, if you have courage enough to risk being swept away by the breakers, going as far out on the reef as you can, you may catch a glimpse of them in their living state—great mounds and masses of what seems rock, but which is a honeycomb of coral, whose cells are filled with the living polypifers. Those in the uppermost cells are usually dead, but lower down they are living.

Always dying, always being renewed, devoured by fish, attacked by the sea—that is the life of a coral reef. It is a thing as living as a cabbage or a tree. Every storm tears a piece off the reef, which the living coral replaces; wounds occur in it which actually granulate and heal as wounds do of the human body.

There is nothing, perhaps, more mysterious in nature than this fact of the existence of a living land: a land that repairs itself, when injured, by vital processes, and resists the eternal attack of the sea by vital force, especially when we think of the extent of some of these lagoon islands or atolls, whose existences are an eternal battle with the waves.

Unlike the island of this story (which is an island surrounded by a barrier reef of coral surrounding a space of sea—the lagoon), the reef forms the island. The reef may be grown over by trees, or it may be perfectly destitute of important vegetation, or it may be crusted with islets. Some islets may exist within the lagoon, but as often as not it is just a great empty lake floored with sand and coral, peopled with life different to the life of the outside ocean, protected from the waves, and reflecting the sky like a mirror.

When we remember that the atoll is a living thing, an organic whole, as full of life, though not so highly organised, as a tortoise, the meanest imagination must be struck with the immensity of one of the structures.

Vliegen atoll in the Low Archipelago, measured from lagoon edge to lagoon edge, is sixty miles long by twenty miles broad, at its broadest part. In the Marshall Archipelago, Rimsky Korsacoff is fifty-four miles long and twenty miles broad; and Rimsky Korsacoff is a living thing, secreting, excreting, and growing—more highly organised than the cocoa-nut trees that grow upon its back, or the blossoms that powder the hotoo trees in its groves.