But old Ocean carries on the work which the polyps have begun. Heavy rollers break incessantly against the reef, loosening blocks of coral, some of which are flung bodily upon it, while others are pounded into sand, which fills up holes and crevices. Gradually thus the whole becomes cemented into hard reef-rock.
As this goes on the low island slowly rises, until it has climbed above high-tide level.
Then the task can only be completed by waves of exceptional reach. Still the grinding of coral to fine sand goes on; and in time it gains a depth of some inches. And the waves carry seeds and cocoa-nuts to the spot; and shrubs and trees spring up, to sow again their own seeds, and by gradual decay to form mould. Thus it comes about that a little island is made ready for man to live on.
One might expect these stages to be very slow indeed, but such events march at the double in tropical climates. In the Low Archipelago one atoll was found, in the space of only thirty-four years, to have been transformed from a mere rock-reef to a lagoon island, fourteen miles in length, with tall trees growing along almost the whole of one side.
As a specimen of the sizes to which coral-buildings reach, the Maldive Archipelago may be named. It is a vast collection of islands and reefs, stretching to a length of four hundred and seventy miles, and in parts fifty miles broad. Barrier-reefs, reaching through many hundreds of miles, are even more remarkable.
Travellers write stirring descriptions of the beauty of these erections. The vivid pen of Miss Gordon-Cumming, for instance, has painted many a picture of Pacific reefs, of thundering breakers, and dazzling white surf.
We are told by her of “the patches of coral, sea-weed, and sometimes white sand, lying at irregular depths beneath a shallow covering of the most crystalline emerald-green water,” producing “every shade of aqua-marine, mauve, sienna, and orange, all marvellously blended.” And, again, of the wonderful masses of living coral which grow like garden-plants below the clear water, and of branching shrubs of all imaginable tints, such as pink, blue, mauve, and primrose.
To pluck and carry off these ocean-blossoms would be a vain attempt, for the “gelatinous slime” to which the colours belong “drips away, as the living creatures melt and die, when exposed to the upper air.”
From the pen of another eye-witness[3] we have a description of a visit at low-tide to the barrier-reef of Levuka, the old Fiji capital. We learn that the reef itself consists mainly of dead coral—“rough, uninteresting, shapeless limestones, with a very small covering of seaweed.” But after about a quarter of a mile of difficult walking, the travellers drew near to the “roaring surf on the outside,” where “fingery lumps of beautiful live coral began to appear, of the palest lavender-blue colour.” By the time that they were nearly within touch of the spray, “the whole floor was one mass of living branches of coral.”
[3] The Hon. Ralph Abercromby.