In front of the eastern MOSQUITO coast, there are between latitude 12 deg and 16 deg some extensive banks (already mentioned, page 148), with high islands rising from their centres; and there are other banks wholly submerged, both of which kinds of banks are bordered, near their windward margins, by crescent-shaped coral-reefs. But it can hardly be doubted, as was observed in the preliminary remarks, that these banks owe their origin, like the great bank extending from the Mosquito promontory, almost entirely to the accumulation of sediment, and not to the growth of corals; hence I have not coloured them.
CAYMAN ISLAND: this island appears in the charts to be fringed; and Captain B. Allen informs me that the reefs extend about a mile from the shore, and have only from five to twelve feet water within them; coloured red.--JAMAICA: judging from the charts, about fifteen miles of the S.E. extremity, and about twice that length on the S.W. extremity, and some portions on the S. side near Kingston and Port Royal, are regularly fringed, and therefore are coloured red. From the plans of some harbours on the N. side of Jamaica, parts of the coast appear to be fringed; but as these are not represented in the charts of the whole island, I have not coloured them.--ST. DOMINGO: I have not been able to obtain sufficient information, either from plans of the harbours, or from general charts, to enable me to colour any part of the coast, except sixty miles from Port de Plata westward, which seems very regularly fringed; many other parts, however, of the coast are probably fringed, especially towards the eastern end of the island.--PUERTO RICO: considerable portions of the southern, western, and eastern coasts, and some parts of the northern coast, appear in the charts to be fringed; coloured red.--Some miles in length of the southern side of the Island of ST. THOMAS is fringed; most of the VIRGIN GORDA Islands, as I am informed by Mr. Schomburgk, are fringed; the shores of ANEGADA, as well as the bank on which it stands, are likewise fringed; these islands have been coloured red. The greater part of the southern side of SANTA CRUZ appears in the Danish survey to be fringed (see also Prof. Hovey's account of this island, in "Silliman's Journal," volume xxxv., page 74); the reefs extend along the shore for a considerable space, and project rather more than a mile; the depth within the reef is three fathoms; coloured red.--The ANTILLES, as remarked by Von Buch ("Descrip. Iles Canaries," page 494), may be divided into two linear groups, the western row being volcanic, and the eastern of modern calcareous origin; my information is very defective on the whole group. Of the eastern islands, BARBUDA and the western coasts of ANTIGUA and MARIAGALANTE appear to be fringed: this is also the case with BARBADOES, as I have been informed by a resident; these islands are coloured red. On the shores of the Western Antilles, of volcanic origin, very few coral-reefs appear to exist. The island of MARTINIQUE, of which there are beautifully executed French charts, on a very large scale, alone presents any appearance worthy of special notice. The south-western, southern, and eastern coasts, together forming about half the circumference of the island, are skirted by very irregular banks, projecting generally rather less than a mile from the shore, and lying from two to five fathoms submerged. In front of almost every valley, they are breached by narrow, crooked, steep-sided passages. The French engineers ascertained by boring, that these submerged banks consisted of madreporitic rocks, which were covered in many parts by thin layers of mud or sand. From this fact, and especially from the structure of the narrow breaches, I think there can be little doubt that these banks once formed living reefs, which fringed the shores of the island, and like other reefs probably reached the surface. From some of these submerged banks reefs of living coral rise abruptly, either in small detached patches, or in lines parallel to, but some way within the outer edges of the banks on which they are based. Besides the above banks which skirt the shores of the island, there is on the eastern side a range of linear banks, similarly constituted, twenty miles in length, extending parallel to the coast line, and separated from it by a space between two and four miles in width, and from five to fifteen fathoms in depth. From this range of detached banks, some linear reefs of living coral likewise rise abruptly; and if they had been of greater length (for they do not front more than a sixth part of the circumference of the island), they would necessarily from their position have been coloured as barrier-reefs; as the case stands they are left uncoloured. I suspect that after a small amount of subsidence, the corals were killed by sand and mud being deposited on them, and the reefs being thus prevented from growing upwards, the banks of madreporitic rock were left in their present submerged condition.
THE BERMUDA Islands have been carefully described by Lieutenant Nelson, in an excellent Memoir in the "Geological Transactions" (volume v., part i., page 103). In the form of the bank or reef, on one side of which the islands stand, there is a close general resemblance to an atoll; but in the following respects there is a considerable difference,--first, in the margin of the reef not forming (as I have been informed by Mr. Chaffers, R.N.) a flat, solid surface, laid bare at low water, and regularly bounding the internal space of shallow water or lagoon; secondly, in the border of gradually shoaling water, nearly a mile and a half in width, which surrounds the entire outside of the reef (as is laid down in Captain Hurd's chart); and thirdly, in the size, height, and extraordinary form of the islands, which present little resemblance to the long, narrow, simple islets, seldom exceeding half a mile in breadth, which surmount the annular reefs of almost all the atolls in the Indian and Pacific Oceans. Moreover, there are evident proofs (Nelson, Ibid., page 118), that islands similar to the existing ones, formerly extended over other parts of the reef. It would, I believe, be difficult to find a true atoll with land exceeding thirty feet in height; whereas, Mr. Nelson estimates the highest point of the Bermuda Islands to be 260 feet; if, however, Mr. Nelson's view, that the whole of the land consists of sand drifted by the winds, and agglutinated together, were proved correct, this difference would be immaterial; but, from his own account (page 118), there occur in one place, five or six layers of red earth, interstratified with the ordinary calcareous rock, and including stones too heavy for the wind to have moved, without having at the same time utterly dispersed every grain of the accompanying drifted matter. Mr. Nelson attributes the origin of these several layers, with their embedded stones, to as many violent catastrophes; but further investigation in such cases has generally succeeded in explaining phenomena of this kind by ordinary and simpler means. Finally, I may remark, that these islands have a considerable resemblance in shape to Barbuda in the West Indies, and to Pemba on the eastern coast of Africa, which latter island is about two hundred feet in height, and consists of coral-rock. I believe that the Bermuda Islands, from being fringed by living reefs, ought to have been coloured red; but I have left them uncoloured, on account of their general resemblance in external form to a lagoon-island or atoll.
INDEX.
The names not in capitals are all names of places, and refer exclusively to the Appendix: in well-defined archipelagoes, or groups of islands, the name of each separate island is not given.
ABROLHOS, Brazil, coated by corals.
Abrolhos (Australia).
ABSENCE of coral-reefs from certain coasts.
Acaba, gulf of.
Admiralty group.
AFRICA, east coast, fringing-reef of. Madreporitic rock of.
Africa, east coast.
AGE of individual corals.
Aiou.
Aitutaki.
Aldabra.
Alert reef.
Alexander, Grand Duke, island.
ALLAN, Dr., on Holuthuriae feeding on corals. On quick growth of corals at Madagascar. On reefs affected by currents.
Alloufatou.
Alphonse.
Amargoura. (Amargura.)
Amboina.
America, west coast.
Amirantes.
Anachorites.
Anambas.
ANAMOUKA, description of.
Anamouka.
Anadaman islands.
Antilles.
Appoo reef.
Arabia Felix.
AREAS, great extent of, interspersed with low islands. Of subsidence and of elevation. Of subsidence appear to be elongated. Of subsidence alternating with areas of elevation.
Arru group.
Arzobispo.
ASCIDIA, depth at which found.
Assomption.
Astova.
Atlantic islands.
ATOLLS, breaches in their reefs. Dimensions of. Dimensions of groups of. Not based on craters or on banks of sediment, or of rock. Of irregular forms. Steepness of their flanks. Width of their reef and islets. Their lowness. Lagoons. General range. With part of their reef submerged, and theory of.
Augustine, St.
AURORA island, an upraised atoll.
Aurora.
AUSTRAL islands, recently elevated.
Austral islands.
Australia, N.W. coast.
AUSTRALIAN barrier-reef.
Australian barrier.
Babuyan group.
Bahama banks.
Balahac.
Bally.
Baring.
BARRIER-REEF of Australia. Of New Caledonia.
BARRIER-REEFS, breaches through. Not based on worn down margin of rock. On banks of sediment. On submarine craters. Steepness of their flanks. Their probable vertical thickness. Theory of their formation.
Bampton shoal.
Banks islands.
Banks in the West Indies.
Bashee islands.
Bass island.
Batoa.
Beaupre reef.
BEECHEY, Captain, obligations of the author to. On submerged reefs. Account of Matilda island.
BELCHER, Captain, on boring through coral-reef.
Belize reef, off.
Bellinghausen.
Bermuda islands.
Beveridge reef.
Bligh.
BOLABOLA, view of.
Bombay shoal.
Bonin Bay.
Bonin group.
BORINGS through coral-reefs.
BORNEO, W. coast, recently elevated.
Borneo, E. coast. S.W. and W. coast N. coast. Western bank.
Boscawen.
Boston.
Bouka.
Bourbon.
Bourou.
Bouton.
BRAZIL, fringing-reefs on coast of.
BREACHES through barrier-reefs.
Brook.
Bunker.
Bunoa.
BYRON.
Cagayanes.
Candelaria.
Cargados Carajos.
Caroline archipelago.
Caroline island.
Carteret shoal.
CARYOPHYLLIA, depth at which it lives.
Cavilli.
Cayman island.
Celebes.
Ceram.
CEYLON, recently elevated.
Ceylon.
CHAGOS Great Bank, description and theory of.
CHAGOS group.
Chagos group.
CHAMA-SHELLS embedded in coral-rock.
CHAMISSO, on corals preferring the surf.
CHANGES in the state of Keeling atoll. Of atolls.
CHANNELS leading into the lagoons of atolls. Into the Maldiva atolls. Through barrier-reefs.
Chase.
China sea.
CHRISTMAS atoll.
Christmas atoll.
Christmas island (Indian Ocean).
Clarence.
Clipperton rock.
COCOS, or Keeling atoll.
Cocos (or Keeling).
Cocos island (Pacific).
COCHIN China, encroachments of the sea on the coast.
Cochin China.
Coetivi.
Comoro group.
COMPOSITION of coral-formations.
CONGLOMERATE coral-rock on Keeling atoll. On other atolls. Coral-rock.
COOK islands, recently elevated.
Cook islands.
CORAL-BLOCKS bored by vermiform animals.
CORAL-REEFS, their distribution and absence from certain areas. Destroyed by loose sediment.
CORAL-ROCK at Keeling atoll. Mauritius. Organic remains of.
CORALS dead but upright in Keeling lagoon. Depths at which they live. Off Keeling atoll. Killed by a short exposure. Living in the lagoon of Keeling atoll. Quick growth of, in Keeling lagoon. Merely coating the bottom of the sea. Standing exposed in the Low archipelago.
CORALLIAN sea.
Corallian sea.
Cornwallis.
Cosmoledo.
COUTHOUY, Mr., alleged proofs of recent elevation of the Low archipelago. On coral-rock at Mangaia and Aurora islands. On external ledges round coral-islands. Remarks confirmatory of the author's theory.
CRESCENT-FORMED reefs.
Cuba.
CUMING, Mr., on the recent elevation of the Philippines.
Dangerous, or Low archipelago.
Danger islands.
DEPTHS at which reef-building corals live. At Mauritius, the Red Sea, and in the Maldiva archipelago. At which other corals and corallines can live.
Dhalac group.
DIEGO GARCIA, slow growth of reef.
DIMENSIONS of the larger groups of atolls.
DISSEVERMENT of the Maldiva atolls, and theory of.
DISTRIBUTION of coral-reefs.
Domingo, St.
DORY, Port, recently elevated.
Dory, Port.
Duff islands.
Durour.
Eap.
EARTHQUAKES at Keeling atoll. In groups of atolls. In Navigator archipelago.
EAST INDIAN ARCHIPELAGO, recently elevated.
Easter.
Echequier.
EHRENBERG, on the banks of the Red Sea. On depths at which corals live in the Red Sea. On corals preferring the surf. On the antiquity of certain corals.
Eimeo.
ELEVATED reef of Mauritius.
ELEVATIONS, recent proofs of. Immense areas of.
Elivi.
ELIZABETH island. Recently elevated.
Elizabeth island.
Ellice group.
ENCIRCLED ISLANDS, their height. Geological composition.
EOUA, description of.
Eoua.
ERUPTED MATTER probably not associated with thick masses of coral-rock.
FAIS, recently elevated.
Fais.
Fanning.
Farallon de Medinilla.
Farson group.
Fataka.
FIJI archipelago.
FISH, feeding on corals. Killed in Keeling lagoon by heavy rain.
FISSURES across coral-islands.
FITZROY, Captain, on a submerged shed at Keeling atoll. On an inundation in the Low archipelago.
Flint.
Flores.
Florida.
Folger.
Formosa.
FORSTER, theory of coral-formations.
Frederick reef.
Freewill.
FRIENDLY group recently elevated.
Friendly archipelago.
FRINGING-REEFS, absent where coast precipitous. Breached in front of streams. Described by MM. Quoy and Gaimard. Not closely attached to shelving coasts. Of east coast of Africa. Of Cuba. Of Mauritius. On worn down banks of rock. On banks of sediment. Their appearance when elevated. Their growth influenced by currents. By shallowness of sea.
Galapagos archipelago.
Galega.
GAMBIER islands, section of.
Gambier islands.
Gardner.
Gaspar rico.
GEOLOGICAL COMPOSITION of coral-formations.
Gilbert archipelago.
Gilolo.
Glorioso.
GLOUCESTER Island.
Glover reef.
Gomez.
Gouap.
Goulou.
Grampus.
Gran Cocal.
GREAT CHAGOS BANK, description and theory of.
GREY, Captain, on sandbars.
