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Updated: June 22, 2025
Some of the atolls, in the larger archipelagoes, stand so near to each other, and have such an evident relationship in form, that they compose little sub-groups: in the Caroline Archipelago, one such sub-group consists of Pouynipete, a lofty island encircled by a barrier-reef, and separated by a channel only four miles and a half wide from Andeema atoll, with a second atoll a little further off.
As the barrier-reef slowly sinks down, the corals will go on vigorously growing upwards; but as the island sinks, the water will gain inch by inch on the shore the separate mountains first forming separate islands within one great reef and finally, the last and highest pinnacle disappearing.
And at the same time, from the formations extending for two thousand miles along the great barrier-reef of Australia formations in which are imbedded nothing but corals, echinoderms, mollusks, crustaceans, and fish, along with an occasional turtle, or bird, or cetacean it might be inferred that there lived in our epoch neither terrestrial reptiles, nor terrestrial mammals.
Seaward, we see the white line of the breakers, indicating the great barrier-reef which surrounds the isle with an almost impenetrable belt; a few channels only lead from the shore to the open ocean. On the 1st of May the Pacific arrived at Nouméa, and her departure for Vila, next day, ended a most tiresome stay. It was a sad, rainy day when we left.
The reef of Mauritius, in front of every river and streamlet, is breached by a straight passage: at Grand Port, however, there is a channel like that within a barrier-reef; it extends parallel to the shore for four miles, and has an average depth of ten or twelve fathoms; its presence may probably be accounted for by two rivers which enter at each end of the channel, and bend towards each other.
If, instead of the island in the diagram, the shore of a continent fringed by a reef had subsided, a great barrier-reef, like that on the north-east coast of Australia, would have necessarily resulted; and it would have been separated from the main land by a deep-water channel, broad in proportion to the amount of subsidence, and to the less or greater inclination of the neighbouring coast-line.
SECTION OF CORAL-REEF. A'A', Outer edges of the barrier-reef at the level of the sea, with islets on it. B'B', The shores of the included island. CC, The lagoon-channel. A''A'', Outer edges of the reef, now converted into an atoll. C', The lagoon of the new atoll.
No one on board knew anything about the island, but they hoped that they might there obtain a fresh supply of water and provisions, and, should it be inhabited by Christians, that they might gain some information as to their direct course for Samoa. Accordingly they steered for an opening which appeared in the barrier-reef.
Here there is a great APPARENT difficulty how were the basal parts of these barrier-reef formed?
It was the island of Raratonga, of which Mr Martin had told Ben. It is surrounded by a curious barrier-reef of solid block coral, thirty-five miles in circumference, and from a quarter of a mile to half a mile broad. At high water it is completely covered to a depth of four or six feet, but at low water it is almost bare. This vast reef prevents the sea from breaking against the island.
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