ON THE STRUCTURE AND DISTRIBUTION OF CORAL REEFS, DARWIN

SHEWING THE DISTRIBUTION -OF THE DIFFERENT KINDS OK COHAI, REEFS TOGETHER WITH THE POSITION OF 'till-: ACTIVE VOLCANO S IN THE MAP {SEE NOTE ffl LEFT HAND CORNER.) fzati: r Note Bright ! Pale blue blue Atolls or lagoon Is?? Barrier Reefs I Red Fringiltg I Verrmhon- spots k Re^s streaks active volcanoes aland 'a S.B Forjurther particulars sec bey uuiiiig of Chap.TI | >0 t IH Wm B 4:5 Ml « Ml lt« and Appendix I" H» -iBtt 60 -— »1 » "" »"» "» * = I t '\0 ON THE STRUCTURE AND DISTRIBUTION OF CORAL REEFS/ BY CHARLES EDITED, DARWIN WITH AN INTRODUC- TION, BY JOSEPH W WILLIAMS LONDON: WALTER SCOTT, NEW YORK : 24 WARWICK EAST 14th STREET LANE THE WALTER SCOTT PRESS, NEWCASTLE-ON-TYNE PREFATORY NOTE In the following pages, first published in 1842, as a companion volume to his Journal of Researches^ Charles Darwin divided coral-reefs into three great classes, each of which is, however, formed upon the same type, and each succeeds the other in general plan of formation 'in much the same way, as childhood passes into youth, and youth into manhood.' The first class, or 'fringing-reef (Fig 1), generally surrounds islands, or skirts Fig 1.— Fringing-Reef and has a channel of shallow water between it and the shore and a gently sloping sea-bed on its The Sandwich Islands, ocean side Examples are numerous great masses of continent, : — the Seychelle Islands, the Solomon Isles, the Friendly Isles, Isles, the New Hebrides, and Mauritius, are margined with this kind of reef; they are also common in the Red Sea, on both its African and Arabian shores, and they form a prolongation from the southern extremity of the promontory of Florida They surround the Nicobar Islands, and skirt nearly the whole of the islands of the West Indies The reefs on the Florida coast are extending inland, and from the rate of their encroachment upon the shore Louis Agassiz has tried the Navigator Natural History Studies, PREFA TOR Y NO TE vi to determine their period of growth, with a result that he would take 1,000 or 1,200 years for coral to of seven fathoms to the surface of the sea; this estimate cannot, however, be universally applicable, since their rate of growth differs in different seas, and varies according to the species Thus, for example, on a ship, which was sunk for twenty months in the Persian Gulf, there was an incrustation of coral to a depth of two feet on her copper bottom; while in the case of the sunken ship Shannon, which was found crusted with coral, it was reckoned that, even supposing the coral to have commenced growing as soon as the ship reached the bottom, the growth could not have been more than three inches in a year Again, some corals have been planted on the Madagascar coast, and these were observed to have grown to a height of nearly three feet in no less than six months The second class, or 'barrier-reef (Fig 2), differs from the first class in that it is situated at a greater distance from the shore, and that, as a consequence of this, the depth of the water on both its littoral and seaward sides is much greater They occur in the middle of the Red Sea; they are common in the Pacific, where they form the great barrier-reef on the north-east coast of Australia, and extend around the Society Islands, the Fijis, and New Caledonia; and they surround islands like the Pelew Islands, and the Comora Isles in the Mozambique considers that it grow upwards from a depth — Channel Some of them are very large; that surrounding New Caledonia is four hundred miles long, and about ten miles distant from the shore; and the one off the north-east coast of Australia is from ten to ninety miles broad, about 1,250 statute miles in length, and rises from the ocean bed on its seaward side from a depth which often exceeds 1,800 Fig 2.— Barrier-Reef feet, PREFA TOR Y NOTE This last VI example of reef has been compared by Jukes to 'a great submarine wall or terrace, fronting the whole north-east coast of Australia, resting at each end on shallow water, but its upper from very great depths about the centre by 10 to 30 fathoms of water, but studded all over with steep-sided block-like masses which rise up to low water-level These masses are especially numerous, and most linear along the edge of the great bank on which they rest; the passage between them being often very narrow, like regular embrasures opened here and there through rising ; surface forming a plateau covered the parapet of wall These a fortress 'individual reefs' running along the outer edge protect the comparatively shallow water inside, and with the numerous inner reefs that are scattered over its space make it one great natural harbour.' The third and last class, or 'atoll' (Fig 3), is an elliptical, oval or roundish ring of coral, with here and there a break in its Fig 3.— Stewart Atoll or Sikiana C, continuity, and with a central as the lagoon The the inside shallow Manual of chap xiii Reef Channel (lat 8° 22' S ; thus off the Geology; p long 162° 58' E.) lake-like expanse of water, outside water ; ; F, Faule Island 131 ; is known generally very deep, and Cocos-Keeling Atoll Voyage of H.M.S Fly, the vol i PREFA TOR Y NOTE viii sounding-lead, at a distance of 2,200 yards from the reefs edge, sinks to a depth of 1,200 fathoms, while the lagoon is only from two to seven fathoms deep channels through the reef ' Such a basin with — affording room enough (as many its of deep, clear them do) Christendom to ride at anchor supplies the very perfection of harbour accommodation, even though the surrounding reefs are so low that during storms the breakers outside will dash over the massed wall of coral In this lagoon marine animals of all sorts including fishes, and pre-eminently sharks swarm but it is seldom that the wind disturbs the water with its smooth, glassy expanse, and curiously enough the openings in the reef are always on the leeward side, that is, in the one least exposed to the prevailing winds, so that while a ship has no difficulty in getting out to sea, it sometimes happens that it does not find an escape from the storm so easy The commonest localities for atolls are the Indian and Pacific Oceans Stewart's atoll (Fig 3) in the Solomon Islands, and the Menschikoff Island may be taken as the for all navies of — — — : typical examples Before Darwin wrote, it was universally believed that these were formed by the coral polypes growing upon submerged volcanic craters This theory finds expression and support in the second volume of Lyell's Principles of Geology, a bonk which was published in 1832, and which Darwin read It is known that he procured the first volume (just then issued) at the suggestion of Henslow previous to his setting out on the voyage of the Beagle, which started from Devonport on atolls December sympathetic friend and probably, too, that kindly, sagacious, and teacher forwarded him the second volume soon as may 27, 1831, as published But whatever case the Darwin was acquainted with the prevailing idea, and that his acute and penetrating mind discerned at once its weaknesses, for he tells us in his Autobiography that the main features of his theory were conceived while on the voyage, and thai even previous to seeing No other work of mine, he says, was a true coral-reef.' Life and Letters of Charles Darwin, 1888, vol p 70 ' be, it is evident ' that ' i PREFA TOR Y NOTE ix in so deductive a spirit as this, for the whole theory was thought out on the west coast of South America, before I had I had only to verify and extend my views seen a true coral-reef But it should be by a careful examination of living reefs observed that I had during the two previous years been incessantly attending to the effects on the shores of South America of the intermittent elevation of the land, together with denudation This necessarily led me to and the deposition of sediment reflect much on the effects of subsidence, and it was easy to replace in imagination the continued deposition of sediment by To this was to form my theory the upward growth of corals of the formation of barrier-reefs and atolls.' Coupled with this, Darwin, as is manifested by his work, also saw that, in forming any theory of the genesis and development of coral-reefs, not only must the nature of the platform on which the corals build be taken into account, but that other factors, of as equally great importance, come into play and must be reckoned, notably, the peculiar conditions of the life of the coral-polypes themselves, begun — and the peculiar, and, then, inexplicable distribution of the reefs He saw more clearly than his precursors had and atolls done the validity of the dictum of Johannes Miiller, in this and indeed in all his works, that the most important truths in Natural Science are to be discovered, neither by the mere analysis of philosophical ideas, nor by simple experience, but by reflective experience, which distinguishes the essential from the accidental in the phenomena observed, and thus finds principles from which many experiences can be derived The conditions necessary for the proper continuance of the organic life of these polypes seem to be a temperature which is not lower than 68°F., the presence of clear water, and a depth not exceeding twenty fathoms They also cannot survive exposure and air, and thus are unable to flourish unless the top of the reef be below the mark of the lowest tides Thus reefs are absent from the West Coast of America because it is washed by a cold extra-tropical current they are not found in the to the sun ; South Atlantic because that ocean is not within their special isotherm; and they are not present on the shores of Trinidad b APPENDIX 264 agglutinated together, were proved correct, this difference would be immaterial; but, from his own account (p 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 embedded the origin stones, with of these several layers, many violent catastrophes; to as their but further investigation in such cases has generally succeeded in phenomena of explaining simpler means Finally, I this may kind by ordinary and 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 consists of coral-rock about 200 feet in height, and 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 in Appendix italics are all names of places, and refer exclusively to the name in well-defined archipelagoes, or groups of islands, the : of each separate island is not given PAGE Abrolhos, corals Brazil, coated 81 2.2.1 Abrolhos {Australia) Absence of from coral-reefs certain coasts Acaba, gulf of Admiralty group Africa, east reef of coast, 84 251 211 fringing- • Madreporitic rock of Africa, east coast Age of individual Aiou Aitutaki Aldabra corals 79 171 240 95, 109 Arabia Felix by 217 192 237 Alert reef 209 Alexander, GrandDuke,island 195 Allan, Dr., on Holuthurise feeding on corals 30 on quick growth of corals at Madagascar 103, 104 —— - reefs affected rents Alloufatou Alphonse Amargura Amboina by cur- XI 202 236 20I 2l8 i*7, 188 America, west coast Amirantes 236 211 Anachorites 226 Anambas Anamouka, description of 167 201 Anamouka Andaman is Ids • 225 Antilles 26l, 262 , Appoo reef 228 PAGE 244 Areas, great extent of, interspersed with low islands 118, of subsidence and of elevation 178, of subsidence appear to be elongated of subsidence alternating with areas of elevations 181, 119 179 179 182 217 2l6 which found 112 236 236 204 Arru group Arzobispo Ascidia, depth at Assomption Astova Atlantic islands Atolls, breaches in their reefs on — — 47, 136, 137 dimensions of 36, 37, 38 dimensions of groups of 118, 119 not based on craters or on banks of sediment, or of rock 115, 116, 120, 121, 122, 181, 182 of irregular forms 36, ^7, 38, 141, 142 steepness of their flanks 38, 39 width of their reef and _ islets their lowness 37, 38 117,118 41, 42, 43 lagoons general range 157, 158 with part of their reef submerged, and theory of 44,45, 136, 137 INDEX 266 PAGE Augustine, St 203 Auroraisland, an upraised atoll " 107, iiS, 175 , Aurora , 189 Austral islands, recently elevated , 166, 174, 175 Austral islands 192 Australia, N IV coast 220 Australian barrier-reef 67, 158 Australian barrier 208 , Bonin group Bahama 229 255, 257 226 222 banks Bat abac Bally Baring 205 Earrier-reef of Australia of New Caledonia 67, 158 71 Barrier-reefs, breaches through 129 not based on worn down margin of rock on banks of sediment 70 7° on submarine craters 71 their probable vertical Banks Banks islds in the West Indies Bashee islds Bass is Id Batoa 194 , Beaupri reef 207 252 229 202 20S Beechey, Captain, obligations of the author to 38 on submerged reefs 40 account of Matilda island IOO Belcher, Captain, on boring through coral-reef 98 Bellinghausen 191 Bermuda islds Bevendge reef , 263 Bligh Bolabola, view of Bombay shoal Benin Bay , 200 207 17 232 224 PAGE 216 Bourbon Bourou Bout on Brazil, fringing-reefs 210 235 218 224 on coast 80 Breaches through barrier-reefs 129 Brook 195 Bunker 195 of Byron , , , .» Cagayanes Candelaria Cargados Carajos Caroline arch thickness 7°s l2 % theory of their formation 127, 128, 129, 130 Bamp'on shoal 209 Bunoa steepness of their flanks 62, 63 Borings through coral-reefs 98, 99 Borneo, W coast, recently elevated 169, 170 Borneo, E coast 223 S W and W coast 226, 227 N coast 227 •western bank 232 201 Boscawen Boston 205 Bouka Babuyan group 226 204 227 210 , , 235 212 -194 217 Caroline isld Carteret shoal Caryophyllia, depth at which it lives Cavilli Celebes 108 Cayma?i Ceram , isld 227 260 219 218 170 233 Ceylon, recently elevated Ceylon Chagos Great Bank, description and theory of 58, 59, 142, 143 Chagos group , 145 Chagos group Chama-shells coral-rock embedded 234 in 105 Chamisso, on corals preferring the surf Changes ing atoll of atolls 87 Keel- in the state of 31 124 INDEX 267 PAGE PAGE leading into the lagoons of atolls 45, 46, the Maldiva atolls 51, 54 through barrier-reefs 129 Corals merely coating the bottom of the sea 81, 82 standing exposed in the Channels Chase China sea 204 231 Christmas atoll 99: 164 Christmas atoll 118 Christmas isld (Indian Ocean) 233 Clarence 195 Clipperton rock 187 Cocos, or Keeling atoll 19 Cocos (or Keeling) 233 Cocos isld (Pacific) 187 Cochin China, encroachments of the sea on the coast 161 Low 233 236 Comoro group 237 Composition of coral formations 148, 149 Conglomerate coral-rock Keeling atoll on other atolls 28 coral-rock islds., recently elevated, Low 43 148 certain areas destroyed by loose sedi arch 158 208 205 237 162 the author's theory Crescent-formed reefs Cuba 162 142 257 Cuming, Mr., on the recent elevation of the Philippines Dangerous, or Danger Low arch islds Depths at 170 188 -195 which reef-building corals live Mauritius, the Red Sea, and in the Maldiva arch at which other corals and 106 at their distribution and absence from ment on coral -rock at Mangaia and Aurora islds 107 on external ledges round coral-islands 134 remarks confirmatory of 165, 174 Cook islds .192 Coral-blocks bored by vermiform animals 30, 149 Coral-reefs, on Cook 162 of recent elevation of the Couthouy, Mr., alleged proofs Cochin China Cornwallis Cosmo ledo Coettvi arch Corallian sea Corallian sea corallines can live no 12 '83 Dhalac group 246 Diego Garcia, slow growth of 89 Dimensions Coral-rock at Keeling atoll 27, 28 Mauritius 77 organic remains of 149 Corals dead but upright in Keeling lagoon 3i depths at which they live 107, 108 Keeling atoll 22 by a short exposure 20 living in the lagoon of Keeling atoll 28, quick growth of, in Keeling lagoon 29 off killed reef -93 the of larger groups of atolls 118, 119 Disseverment of the Maldiva atolls, and theory of 58, 139 Distribution of coral-reefs 83 Domingo, St Dory, Port, recently elevated Dory, Port Duff islds Durour 261 169 216 208 212 Eap Earthquakes at Keeling atoll 214 34 INDEX 263 PAGE Earthquakes groups in Flint of 125, 126 Navigator arch 168 East Indian arch., recently elevated 169 Easter iSS Echequier 211 Ehrenberg, on the banks of the Red Sea 81, 245 on depths at which corals live in the Red Sea no on corals preferring the atolls surf ^7 on the antiquity of certain Eimeo corals Flores in 96 189 Elevated reef of Mauritius 77 Elevations, recent proofs of 164 immense areas of 178, 179 Elivi 214 Elizabeth isld 98 recently elevated 165, 176 Elizabeth isld .188 I Florida Folger Formosa | ! i Forster, theory of coral-formations 122 Frederick reef 209 Freewill 217 Friendly group recently elevated 167, 177 Friendly arch .200 Fringing-reefs, absent where coast precipitous breached in streams described by Ellice group Encircled , their height geol composition 66 6S, 70, 71 Eoua, description of Eoua 203 islds 167 of coral-rock Fais, recently elevated 168, 175 Fiats Fanning Farallon de Medinilla 214 197 215 Farsan group 246, 247 Fataka 207 Fiji arch 202 Fish, feeding on corals 30 Fish killed in Keeling lagoon by heavy rain 36 Fissures across coral-islds 126 ; Fitzroy, Capt shed — — , on a submerged Keeling atoll on an inundation in the at Low arch 34 124 90 MM Quoy 165 appearance their 81 80 • section of composition Geological coral-formations Gilbert arch Gilolo • Gloriosa Gloucester isld Glover reef Gomez Gouap islds Gaspar-Rico 81 influenced Galapagos arch Galega islds., 80 77 growth by currents by shallowness of sea Gambier Gambler Gardner 75 79 7S 73 when elevated their 149 of 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 200 Erupted matter probably not associated with thick masses 73, 74 front and Gaimard PAGE 194 222 256 216 229 188 236 69 189 196 205 of [48, 149 204 219 236 124 260 188 214 INDEX 269 PAGE Goulou 214 Juan 216 Grampus Cocal 203 Great Chagos Bank, description and theory of 58, 142 Grey, Capt , on sandbars 76 Grouping of the different Gra.fi classes of reefs Guedes 157 217 Hall, Capt B., on Loo Choo 170 islds., recently elevated -174 Height of encircled islds 66 Her mites 211 Ha?-vey or Cook islds .192 Harvey de Nova {Madagascar) Kalatoa Kamtschatka, of proofs recent elevation Karkalang Keeling 223 its of reef atoll, section Keeling, south atoll north atoll Keffing PAGE 239 178 219 19 233 33 218 194, 196 208 Kemin Kennedy Keppel 121 Kumi 230 Hogoleu Holuthurise feeding on coral isld., height of Honduras , reef off Honden 118 Horn Houtmari s Abrolhos Huaheine; alleged proofs its recent elevation Htiaheine Hunter Hurricanes, 2.2.1 coral-islds .191 Imrnaum of, 202 124 244 203 recently elevated India 195 on Independence India, west coast, 174 effects 259 202 of Humphrey 212 30 Irregular reefs in shallow seas Islets of coral-rock, their for- mation Jamaica Jarvis Java, recently elevated Java Johnston Juan de isld Nova , , cently elevated 80 168 of their formation 48, 132, 133 of small atolls filled up with sediment 49, 50 Lagoon-channels within barrier-reefs 63, 64 Lagoon-reefs, all submerged in some atolls, and rising to the surface in others Lancaster reef Latie Lauglan islds Ledges round certain lagoons, 261 195 169 92 194 201 209 48, 133 Lette Lighthouse reef Lloyd, Mr., on corals refixing themselves Loo Choo, recently elevated Loo Choo Louisiade 56 234 26 re- Ladrones arch 215 Lagoon of Keeling atoll 28 Lagoons bordered by inclined ledges and walls, and theory 170 245 their destruction in the Maldiva atolls Laccadive group Ladrones, or Marianas, Low 220 260 104 170 230 209 197 archipelago, alleged proofs of its recent elevation 162 Low arch .188 Lowness of coral-islds .118 237 Loyalty group 222 208 INDEX 270 PAGE Lucepara 226 Adm , on fissures across coral-islands 126 , Luzon, recently elevated 170 Lutke, Luzon Mr., on channels into the lagoons of atolls on the lowness of their 228 Lyell, leeward sides on the antiquity of tain corals — on 47 137 96 con- 215 215 191 arch Mariere Marquesas arch Marshall arch Marshall isld Martinique , Mart ires 216 215 isld Matia, or Aurora Matilda atoll , islands , 149 on the recently elevated beds of the Red Sea 172 on the outline of the areas of subsidence 179 sir Macclesfield bank 223 231 , Madagascar, quick growth of corals at madreporitic rock of Madagascar Madjiko-sima Madura Madura {Java) {India) Mahlos Mahdoo, theory formation Malacca, recently elevated Malacca Malcolmson, 103 171 239 229 222 233 live there recently elevated isld recently elevated Mangaia Mangs • 170 235 69 190 37, 142 • Mendana Menaana atoll arch isles 91 , 234 • 216 16S 208 Mexico, gulf of -255 Millepora complasata at Keeling atoll Mifidoro 228 21 Mohilla Molucca Morty 238 islands, recently ele- 169 Moresby, Capt., on through coral-reefs 107 148, 175 193 Marianas, recently elevated Menchikoff 171 226 73 Mauritius Maurua, section of Mopeha arch 100 io6, 107 139 Dr., on recent elevation of W coast of India 169 on recent elevation of Camaran isld 172 Maiden 195 Maldiva atolls, and theory of their formation 44, 134, 135, 139 steepness of their flanks 39 growth of coral at 103 Maldiva Mangaia vated of 89 depths at which corals Maurua Macassar 262 196 ,189 Mauritius, fringing-reefs of tinuity of distinct coral- 204 Mary's St in Madagascar, harbour made in reefs Mary cer- apparent the PAGE Mariana , Mosquito coast Musquillo atoll 191 boring 99 219 Mysol 260 141 218 Namourrek Natunas group Navigator arch., elevation Navigator arch Nederlandisch 141 of 226 168 199 209 Nelson, Lieut., on the consolidation of coral-rocks under water theory of coral-forma tions 98 122 INDEX 271 PAGE Nelson, Lieut., on the muda New New its islds Ber- 263 211 Britain 62 barrier-reef of 71? J 32 140, 158 New Caledonia Netv Guinea (E end) New Gttinea ( W end) New Hanover New Hebrides, 211 217 210 vated 208 recently ele- 168 New Hebrides 205 New Ireland, recently elevated 168 New Ireland 205 New Na7itucket 196 Nicobar islds Niouha Nulliporse at Keeling atoll on the reefs of atolls 235 201 24 42 62 on barrier-reefs their wide distribution and abundance 115 Objections to the theory of subsidence , i Outong Java 194 Peregrino - .194 at 76 Persian gulf, recently elevated 172 Persian gulf Pescado 244 195 Pescadores 230 Peyster group 203 Philip 214 Philippine arch., recently elevated 170 Philippine arch 227 , Phcenix Piguiram , , , Pitcairn Pitt's bank Pitt isld Platte Pleasant Porites, chief coral of Keeling atoll Postillions 196 213 189 144 204 236 204 on margin 20 223 160 Pouynipete its probable subsidence 161 Pouynipete 212 Prat as shoal 231 Proby 202 Providence 236 Puerto Rico 261 Pulo Anna 215 Pumice floated to coral-islds 149 146 98, 204 Ocean islds 202 Ono 202 Onouafu Ormuz 244 Oscar group 203 Oscillations of level 173, 174, 182 212 Ouallan or Ualan , 101 Ouluthy atoll PAGE 242 Pernambuco, bar of sandstone Caledonia, steepness of reef Pemba Penrhyn 210 Pylstaart Pyrard de 200 Laval, astonishment at the atolls in the Indian Ocean 15 Palawan, S W coast N W coast western bank , Palmerston Palmyra Paracells Paraquas Patchow Pelew islds Pemba isld , , Quoy and at Gaimard, depths which corals live Ill 192 197 231 232 229 Range 214 Rapa , , 226 227 232 singular form of 171 description of reefs applicable only to fringing-reefs of atolls Pearson , 165 159 194 195 INDEX 272 Red Sea, banks of rock coated by reefs proofs of tion 81 its recent eleva- 171 supposed subsidence of 173 Red Sea 245 Reefs, irregular in shallow seas So rising to the surface in some lagoons, and submerged in others their distribution 92 S3 from some their absence coasts Revilla-gigedo 84 187 reefs of the Maldiva atolls, and theory of 52, 134 Rotches Rotoumah Roug , Rowley shoals , Dr., on the deposits of Red Sea Riippell, He de Sahia de Malha Sable, recent Si! Pierre Sala Salomon arch Samoa, or Navigator elevation of arch Samoa Sanserot 209 168 188 arch 235 234 arch., Sandal-wood Sandwich arch., recently vated 171 236 Sand-bars parallel to coasts Sandwich 235 216 199 204 203 212 221 199 76 220 ele- 165 197 215 Santa-Cruz group 207 Savage isld., recently elevated, 98, 167, 175 Savage Savu Saya, or Sahia de Malha Scarborough shoal 221 Scoffs reef Sections of islands encircled by barrier-reefs 69, 128 128 of Bolabola Sediment in Keeling lagoon 29 in other atolls 43, 54, 55 injurious to corals 89 transported from coral Ring-formed Rodriguez Rosario Rose isld PAGE 3° 211 Scilly 191 Scoria? floated to coral-islds 149 all Scarus feeding on corals Schouten 200 220 234 232 islands far seaward Seniavi7ie 149 212 219 235 Serajigani Seychelles Ship-bottom with coral Smyth isld quickly coated 104 197 , Society arch., stationary 162 dition of alleged proofs of recent elevation 174 Society arch 189 Socotra 244 222 Solor Soolooislds., recently elevated 170 Sooloo islds 227 Souvaroff Spanish Sponge, depths at which found Starbuck Stones transported in roots of trees 149 Storms, effects of, on coral 124 islds Stutchbury, Mr., on the growth of an Agaricia on upraised corals in Society arch Subsidence of Keeling atoll extreme slowness of 146 areas of, apparently elon gated areas of immense great amount of Suez, gulf of 195 215 112 194 105 174 42 182 179 178, 179 181, 190 251 INDEX 273 PAGE PAGE Sulphur islds .216 Sumatra, recently elevated 169 Sumatra Stcmbawa 224 222 Surf favourable to the growth of massive corals Swallow shoal Sydney is Id 87 232 196 Vanikoro, section of 69 Vanikoro, its state and changes in reefs its Vanikoro Vine reef Virgin Gorda Viti arch 207 209 261 161 202 Volcanic islands, with living on their shores 84 matter, probably not associated with thick masses of coral-rock 148 corals Tahiti, alleged proofs of its recent elevation Tahiti Temperature of the sea Galapagos arch Tenasserim Tenimber is Id 174 189 at the 84 226 217 Teturoa 190 Theories on coral-formations 115 122 Theory of subsidence, and objections to 120, 145 Thickness, vertical, of barrierreefs 69, 128 Jhomas, St 261 Tikopia 207 Timor, recently elevated 169 Timor 219 Timor-latit 217 Tokan-Bessees 223 Tongatabou 200 Tonquin 233 Toubai Toufoa 191 201 207 Toupoua Volcanoes, authorities for their position on the map 151, 152, 153 deterpresence mined by the movements in progress 175 absent or extinct in the areas of subsidence I TJ, 178 their Waigiou Wallis isld Washington Wells' reef .201 rock embedded exposed in the arch Tumbelan Tumeffe reef Ttirtle Ualan corals Wolchonsky 149 Wo stock 162 105 Xulla 226 360 202 York isld Yucutan, coast of Low Tubular ia, quick growth of on antiquity of certain in coral- left 123 islds Triclacnse 197 209 Wellstead, Lieut., account of a ship coated with corals 104 West Indies, banks of sediment fringed by reefs 81 recently elevated 172 West Indies 252 Whitsunday isld., view of 16 changes in its state 125 Williams, Rev J., on traditions of the natives regarding coral-islds 123 Traditions of change in coral- 217 212 islds Zones corals reefs 107 188 194 , • 218 196 259 of different kinds 0/ outside the same 91, 883 101 On Certain Areas of Elevation and Subsidence in the Pacific and Indian Oceans, as deduced from the Study of Coral Formations —A Paper read Geological Society on Charles Darwin, -5 F.G.S before the {Abstract, reprinted'/rem the 11 May Proceedings" 31st, 1837, by vol ii.pp 552-554.) The author commenced by observing on some of the most remarkable points in the structure of lagoon islands He then proceeded to show that the lamelliform corals, the only efficient and agents in forming a reef, not grow at any great depths that beyond twelve fathoms the bottom generally consists of calcareous sand, or of masses of dead coral rock As long as lagoon islands were considered tne only difficulty to be solved, the belief that corals constructed their habitations (or speaking more correctly, their skeletons) on the crests of submarine craters, was both plausible and very ingenious ; although the immense size, sinuous outline, and great number, must have startled any one who adopted this theory Mr Darwin remarked that a class of reefs which he calls " encircling" are quite, if not more, extraordinary These form a ring round mountainous islands, at the distance of two and three miles from the shore; rising on the outside from a profoundly deep ocean, and separated from the land by a channel, frequently about 200 and sometimes 300 feet deep This structure as observed by Balbi resembles a lagoon, or an atoll, surrounding another island In this case it is impossible, on account of the nature of the central mass, to consider the reef as based on an external crater, or on any accumulation of sediment for such reefs encircle the submarine prolongation of islands, as well as the Of this case New Caledonia presents an islands themselves extraordinary instance, the double line of reef extending 140 ; ; CORAL FORMATIONS 276 miles beyond the island Again the barrier-reef, running for nearly iooo miles parallel to the North-East coast of Australia, and including a wide and deep arm of the sea, forms a third class, and is the grandest and most extraordinary coral formation in the world barrier The and lagoon, reef itself in the three classes, encircling, is most closely similar the difference ; absence or presence of neighbouring land, and the relative position which the reefs bear to it The author particularly points out one difficulty in understanding the structure in the barrier and encircling classes, namely, that the reef extends so far from the shore, that a line drawn perpendicularly from its outer edge down to the solid rock on which the reef must be based, very far exceeds that small limit at which corals can grow A distinct class of however exists, which the author reefs calls "fringing reefs," which extend only so far from the shore, that there is no difficulty in understanding their growth The theory which Mr Darwin then offered, so as to include every kind of structure, is simply that as the land with the attached reefs subsides very gradually from the action of subterranean causes, the coral-building polypi soon again raise their solid masses to the level of the water but not so with the land each inch lost As the whole gradually sinks, the is irreclaimably gone water gains foot by foot on the shore, till the last and highest Before explaining this view in peak is finally submerged offered some considerations on the probability detail, the author such as the small portion of land in of general subsidences, the Pacific, where many causes tend to its production, an argument first suggested by Mr Lyell, and the extreme entirely lying in the ; : ; — — difficulty (with the knowledge that corals grow at but limited depths) in explaining the existence of a vast number of reefs on one level, without we grant subsidence, so that one mountain the zoophytes always top should be submerged after another ; bringing up their stony masses to the surface of the water Subsidence being thus rendered almost necessary, it was shown by the aid of sections, that a simple fringing reef would thus necessarily be converted by the upward growth of the coral into CORAL FORMATIONS 277 one of the encircling order, and this finally, by the disappearance through the agency of the same movement of the central In the former manner a reef skirting land, into a lagoon island into a barrier extending parallel to, a shore would be changed but at same distance from, the mainland Mr Darwin then showed that there existed every intermediate form between a simple well -characterised encircling reef, and a lagoon island ; that New Caledonia supplied a link between encircling and barrier reefs that the different reefs produced by the same order of movement were always in juxtaposition, of which the Australian barrier associated with He encircled islets and true lagoons, affords a good example then proceeded to show that within the lagoon of Keeling Island, proofs of subsidence might be deduced from many ; falling trees and a ruined storehouse ; these movements appear- ing to take place at the period of bad earthquakes, which miles distant It was thence Sumatra rises (of which proofs are well known to exist), the other end of the level sinks down Keeling Island thus acting as an index of the movement of the bottom of the Indian Ocean Again at Vanikoro, where the likewise affect Sumatra, 600 inferred as probable, that as ; structure indicates, according to the theory, recent subsidence, known lately to have occurred The author then removed an apparent objection violent earthquakes are the to would form a disc of coral, but cup-shaped mass or lagoon, not a by showing that corals which grow in tranquil water are very different from those on the outside, and less effective and that as the basin became shallower theory, namely, that subsidence ; they are subject to various causes of injury The lagoon nevertheless is constantly filling up to the height of lowest water spring tides (the utmost possible limit of living coral), and in that state it long remains, for no means exist to complete the work Mr Darwin then proceeded to the main object of the paper, in showing that as continental elevations act over wide areas, so might we suppose continental subsidences would do, and in conformity to these views, that the Pacific and Indian seas could be divided into symmetrical areas of the two kinds the ; CORAL FORMATIONS 278 one sinking, as deduced from the presence of encircling and barrier-reefs, and lagoon islands, and the other rising, as known from uplifted shells and corals, and skirting reefs The absence of lagoon islands in certain wide tracts, such as in both the West and East Indies, Red Sea, etc., was thus easily explained, for proofs of recent elevation are there abundant In a like manner, in very many cases where islands are only fringed with reefs, which according to the theory had not been subsiding, actual proofs of elevation were adduced Mr Darwin remarked that, excepting on the theory of the configuration of reefs being determined by the order of movement, the circumstance that certain classes which are characteristic and universal in some parts of the sea, being never found in others, is quite anomalous, and has never been attempted to be explained Mr Darwin then pointed out the above areas, both in the Pacific and Indian Oceans, and deduced the following as the principal results ist That linear spaces of great extent are undergoing movements of an astonishing uniformity, and that From an the bands of elevation and subsidence alternate extended examination, that the points of eruption all fall on the areas of elevation The author insisted on the importance of this law, as thus affording some means of speculating, wherever volcanic rocks occur, on the changes of level even during ancient geological periods That certain coral formations : — monuments over subsided land, the geographical consequent on geological changes as laid down by Mr Lyell) is elucidated, by the discovery of former centres, whence the germs could be disThat some degree of light might thus be seminated thrown on the question, whether certain groups of living beings peculiar to small spots are the remnants of a former large population, or a new one springing into existence Lastly, when beholding more than a hemisphere, divided into symmetrical areas, which within a limited period of time have undergone acting as distribution of organic beings (as certain known movements, we obtain system by which the crust of the globe endless cycle of changes some is insight into the modified during the ... sustain the coral theory of formation as propounded by Agassiz They prove, on the contrary, that the coral tract of Florida is confined to a border region on the south and south-east, and there... limestone of lime within its mass and has, therefore, overstated the destructive agency of the sea Secondly, the growth of corals, and the consequent formation of coral- rock within the lagoon,... Sea, on both its African and Arabian shores, and they form a prolongation from the southern extremity of the promontory of Florida They surround the Nicobar Islands, and skirt nearly the whole of