INDEX TO VOLCANIC ISLANDS.

Abel, M., on calcareous casts at the Cape of Good Hope 261 Abingdon island 234 Abrolhos islands, incrustation on 188 Aeriform explosions at Ascension 191 Albatross, driven from St. Helena 225 Albemarle island 234 Albite, at the Galapagos archipelago 234 Amygdaloidal cells, half filled 184 Amygdaloids, calcareous origin of 176 Ascension, arborescent incrustation on rocks of 188 —— absence of dikes, freedom from volcanic action, and state of lava-streams 226 Ascidia, extinction of 258 Atlantic Ocean, new volcanic focus in 226 Augite, fused 239 Australia 251 Azores 182, 248 Bahia in Brazil, dikes at 247 Bailly, M., on the mountains of Mauritius 185 Bald Head 260 Banks’ Cove 234, 236 Barn, The, St. Helena 216 Basalt, specific gravity of 245 Basaltic coast-mountains at Mauritiu 185 —— at St. Helena 218 —— at St. Jago 178 Beaumont, M. Elie de, on circular subsidences in lava 233 —— on dikes indicating elevation 228 —— on inclination of lava-streams 227 —— on laminated dikes 212 Bermuda, calcareous rocks of 260, 262 Beudant, M., on bombs 191 —— on jasper 197 —— on laminated trachyte 211 —— on obsidian of Hungary 207 —— on silex in trachyte 270, 197 Bole 257 Bombs, volcanic 189 Bory St. Vincent, on bombs 190 Boulders, absence in Australia and Cape of Good Hope 265 Brattle island 238 Brewster, Sir D., on a calcareo-animal substance 201 —— on decomposed glass 252 Brown, Mr. R., on extinct plants from Van Diemen’s land 257 —— on sphærulitic bodies in silicified wood 207 Buch, Von, on cavernous lava 233 —— on central volcanoes 249 —— on crystals sinking in obsidian 243 —— on laminated lava 209 —— on obsidian streams 208 —— on olivine in basalt 234 —— on superficial calcareous beds in the Canary islands 224 Calcareous deposit at St. Jago affected by heat 169, 171 —— fibrous matter, entangled in streaks in scoriæ 174 —— freestone at Ascension 198 —— incrustations at Ascension 199 —— sandstone at St. Helena 222 —— superficial beds at King George’s sound 260 Cape of Good Hope 263 Carbonic acid, expulsion of, by heat 171, 176 Carmichael, Capt., on glassy coatings to dikes 216 Casts, calcareous, of branches 261 Chalcedonic nodules 257 Chalcedony in basalt and in silicified wood 196 Chatham island 231, 235, 241, 248, 259 Chlorophæite 257 Clarke, Rev. W., on the Cape of Good Hope 258, 263 Clay-slate, its decomposition and junction with granite at the Cape of Good Hope 264 Cleavage of clay-slate in Australia 252 Cleavage, cross, in sandstone 253 Coast denudation at St. Helena 226 Columnar basalt 173 “Comptes Rendus,” account of volcanic phenomena in the Atlantic 226 Concepcion, earthquake of 228, 249 Concretions in aqueous and igneous rocks compared 206 —— in tuff 197 —— of obsidian 206, 208 Conglomerate, recent, at St. Jago 181 Coquimbo, curious rock of 261 Corals, fossil, from Van Diemen’s Land 256 Crater, segment of, at the Galapagos 238 —— great central one at St. Helena 219 —— internal ledges round, and parapet on 220 Craters, basaltic, at Ascension 189 —— form of, affected by the trade wind 189 —— of elevation 227 —— of tuff at Terceira 182 —— of tuff at the Galapagos archipelago 230, 231, 235, 237 —— their breached state 240 —— small basaltic at St. Jago 177 —— —— at the Galapagos archipelago 232 Crystallisation favoured by space 211 Dartigues, M., on sphærulites 207 Daubeny, Dr., on a basin-formed island 237 —— on fragments in trachyte 193 D’Aubuisson on hills of phonolite 222 —— on the composition of obsidian 206 —— on the lamination of clay-slate 210 De la Beche, Sir H., on magnesia in erupted lime 174 —— on specific gravity of limestones 198 Denudation of coast at St. Helena 226 Diana’s Peak, St. Helena 220 Dieffenbach, Dr., on the Chatham Islands 259 Dikes, truncated, on central crateriform ridge of St. Helena 219 —— at St. Helena; number of; coated by a glossy layer; uniform thickness of 216 —— great parallel ones at St. Helena 222 —— not observed at Ascension 226 —— of tuff 231 —— of trap in the plutonic series 247 —— remnants of, extending far into the sea round St. Helena 226 Dislocations at Ascension 192 —— at St. Helena 217, 221 Distribution of volcanic islands 248 Dolomieu, on decomposed trachyte 182 —— on laminated lava 210, 211 —— on obsidian 208 Drée, M., on crystals sinking in lava 243 Dufrenoy, M., on the composition of the surface of certain lava-streams 209, 243 —— on the inclination of tuff-strata 236 Eggs of birds embedded at St. Helena 224 —— of turtle at Ascension 198 Ejected fragments at Ascension 192 —— at the Galapagos archipelago 239 Elevation of St. Helena 225 —— the Galapagos archipelago 241 —— Van Diemen’s Land, Cape of Good Hope, New Zealand, Australia, and Chatham island 258 —— of volcanic islands 250 Ellis, Rev. W., on ledges within the great crater at Hawaii 220 —— on marine remains at Otaheite 184 Eruption, fissures of 224, 249, 250 Extinction of land-shells at St. Helena 224 Faraday, Mr., on the expulsion of carbonic acid gas 171 Feldspar, fusibility of 246 —— in radiating crystals 263 —— Labrador, ejected 193 Feldspathic lavas 179 —— at St. Helena 219 —— rock, alternating with obsidian 202 —— lamination, and origin of 209 Fernando Noronha 181, 210 Ferruginous superficial beds 259 Fibrous calcareous matter at St. Jago 174 Fissures of eruption 242, 249, 250 Fitton, Dr., on calcareous breccia 262 Flagstaff Hill, St. Helena 216 Fleurian de Bellevue on sphærulites 207 Fluidity of lavas 234, 235 Forbes, Professor, on the structure of glaciers 212 Fragments ejected at Ascension 192 —— at the Galapagos archipelago 239 Freshwater Bay 238, 243 Fuerteventura (Feurteventura), calcareous beds of 224 Galapagos archipelago 229 —— parapets round craters 220 Gay Lussac, on the expulsion of carbonic acid gas 171 Glaciers, their structure 212 Glossiness of texture, origin of 206 Gneiss, derived from clay-slate 264 —— with a great embedded fragment 252 Gneiss-granite, form of hills of 259 Good Hope, Cape of 263 Gorges, narrow, at St. Helena 225 Granite, junction with clay-slate, at the Cape of Good Hope 263 Granitic ejected fragments 192, 239 Gravity, specific, of lavas 243-8 Gypsum, at Ascension 201 —— in volcanic strata at St. Helena 215 —— on surface of the ground at ditto 223 Hall, Sir J., on the expulsion of carbonic acid gas 171 Heat, action of, on calcareous matter 170 Hennah, Mr., on ashes at Ascension 189 Henslow, Prof., on chalcedony 197 Hoffmann, on decomposed trachyte 182 Holland, Dr., on Iceland 228 Horner, Mr., on a calcareo-animal substance 201 —— on fusibility of feldspar 246 Hubbard, Dr., on dikes 247 Humboldt on ejected fragments 193 —— on obsidian formations 207, 209 —— on parapets round craters 220 —— on sphærulites 210 Hutton on amygdaloids 176 Hyalite in decomposed trachyte 182 Iceland, stratification of the circumferential hills 228 Islands, volcanic, distribution of 248 —— their elevation 250 Incrustation, on St. Paul’s rocks 187 Incrustations, calcareous, at Ascension 199 Jago, St. 167 James island 234, 237, 242 Jasper, origin of 196 Jonnès, M. Moreau de, on craters affected by wind 189 Juan Fernandez 250 Keilhau, M., on granite 264 Kicker Rock 232 King George’s sound 259 Labrador feldspar, ejected 193 Lakes at bases of volcanoes 229 Lamination of volcanic rocks 209 Land-shells, extinct, at St. Helena 224 Lanzarote, calcareous beds of 223 Lava, adhesion to sides of a gorge 177 —— feldspathic 179 —— with cells semi-amygdaloidal 184 Lavas, specific gravity of 243, 247 Lava-streams blending together at St. Jago 177 —— composition of surface of 208 —— differences in the state of their surfaces 244 —— extreme thinness of 238 —— heaved up into hillocks at the Galapagos archipelago 233 —— their fluidity 234, 235 —— with irregular hummocks at Ascension 189 Lead, separation from silver 244 Lesson, M., on craters at Ascension 189 Leucite 234 Lime, sulphate of, at Ascension 200 Lonsdale, Mr., on fossil-corals from Van Diemen’s land 256 Lot, St. Helena 221 Lyell, Mr., on craters of elevation 227 —— on embedded turtles’ eggs 198 —— on glossy coating to dikes 216 Macaulay, Dr., on calcareous casts at Madeira 262 MacCulloch, Dr., on an amygdaloid 184 —— on chlorophæite 287 —— on laminated pitchstone 209 Mackenzie, Sir G., on cavernous lava-streams 233 —— on glossy coatings to dikes 216 —— on obsidian streams 208 —— on stratification in Iceland 228 Madeira, calcareous casts at 262 Magazine, Nautical,—account of volcanic phenomena in the Atlantic 226 Marekanite 206 Mauritius, crater of elevation of 184, 227 Mica, in rounded nodules 168 —— origin in metamorphic slate 264 —— radiating form of 263 Miller, Prof., on ejected Labrador feldspar 193 —— on quartz crystals in obsidian beds 202 Mitchell, Sir T., on bombs 191 —— on the Australian valleys 254 Mud streams at the Galapagos archipelago 236 Narborough island 234 Nelson, Lieut., on the Bermuda islands 260, 262 New Caledonia 248 New Red sandstone, cross cleavage of 253 New South Wales 251 New Zealand 259 Nulliporæ (fossil), resembling concretions 169 Obsidian, absent at the Galapagos archipelago 241 —— bombs of 191 —— composition and origin of 207, 208 —— crystals of feldspar sink in 243 —— its irruption from lofty craters 246 —— passage of beds into 202 —— specific gravity of 243, 246 —— streams of 208 Olivine decomposed at St. Jago 178 —— at Van Diemen’s land 257 —— in the lavas at the Galapagos archipelago 234 Oolitic structure of recent calcareous beds at St. Helena 223 Otaheite 183 Oysters, extinction of 258 Panza islands, laminated trachyte of 209 Pattinson, Mr., on the separation of lead and silver 244 Paul’s, St., rocks of 187 Pearlstone 206 Peperino 232 Péron, M., on calcareous rocks of Australia 262, 263 Phonolite, hills of 179, 181, 221 —— laminated 210 —— with more fusible hornblende 246 Pitchstone 204 —— dikes of 209 Plants, extinct 257 Plutonic rocks, separation of constituent parts of, by gravity 246 Porto Praya 167 Prevost, M. C., on rarity of great dislocations in volcanic islands 217 Prosperous hill, St. Helena 218 Pumice, absent at the Galapagos archipelago 241 —— laminated 209, 210, 211 Puy de Dome, trachyte of 193 Quail island, St. Jago 168, 170, 173 Quartz, crystals of, in beds alternating with obsidian 202 —— crystallised in sandstone 252 —— fusibility of 246 —— rock, mottled from metamorphic action with earthy matter 170 Red hill 173 Resin-like altered scoriæ 171 Rio de Janeiro, gneiss of 252 Robert, M., on strata of Iceland 228 Rogers, Professor, on curved lines of elevation 249 Salses, compared with tuff craters 240 Salt deposited by the sea 200 —— in volcanic strata 201, 215 —— lakes of, in craters 240 Sandstone of Brazil 265 —— of the Cape of Good Hope 265 —— platforms of, in New South Wales 252, 265 Schorl, radiating 263 Scrope, Mr. P., on laminated trachyte 209, 210, 212 —— on obsidian 208 —— on separation of trachyte and basalt 244 —— on silex in trachyte 176 —— on sphærulites 210 Seale, Mr., geognosy of St. Helena 215 —— on dikes 226 —— on embedded birds’ bones 225 Seale, on extinct shells of St. Helena 224 Sedgwick, Professor, on concretions 206 Septaria, in concretions in tuff 198 Serpulæ on upraised rocks 185 Seychelles 248 Shells, colour of, affected by light 201 —— from Van Diemen’s land 256 —— land, extinct, at St. Helena 224 —— particles of, drifted by the wind at St. Helena 223 Shelly matter deposited by the waves 200 Siau, M., on ripples 254 Signal Post Hill 168, 175, 176 Silica, deposited by steam 182 —— large proportion of, in obsidian 206, 208 —— specific gravity of 246 Siliceous sinter 196 Smith, Dr. A., on junction of granite and clay-slate 264 Spallanzani on decomposed trachyte 182 Specific gravity of recent calcareous rocks and of limestone 198 —— of lavas 245 Sphærulites in glass and in silicified wood 207 —— in obsidian 204, 210 Sowerby, Mr. G. B., on fossil-shells from Van Diemen’s land 256 —— from St. Jago 169 —— land-shells from St. Helena 224 St. Helena 214 —— crater of elevation of 227 St. Jago, crater of elevation of 227 —— effects of calcareous matter on lava 231 St. Paul’s rocks 187, 248 Stokes, Mr., collections of sphærulites and of obsidians 207, 212 Stony-top, Little 218, 222 —— Great 218 Stratification of sandstone in New South Wales 253, 255 Streams of obsidian 208 Stutchbury, Mr., on marine remains at Otaheite 184 Subsided space at Ascension 192 Tahiti 183 Talus, stratified, within tuff craters 236 Terceira 182 Tertiary deposit of St. Jago 169 Trachyte, absent at the Galapagos archipelago 241 —— at Ascension 193 —— at Terceira 182 —— decomposition of, by steam 182 —— its lamination 200, 210 —— its separation from basalt 244 —— softened at Ascension 194 —— specific gravity of 245 —— with singular veins 195 Trap-dikes in the plutonic series 247 —— at King George’s sound 259 Travertin at Van Diemen’s land 257 Tropic-bird, now rare, at St. Helena 225 Tuff, craters of 231, 235, 236 —— their breached state 240 —— peculiar kind of 231 Turner, Mr., on the separation of molten metals 244 Tyerman and Bennett on marine remains at Huaheine 184 Valleys, gorge-like, at St. Helena 225 —— in New South Wales 254 —— in St. Jago 180 Van Diemen’s land 256 Veins in trachyte 195 —— of jasper 195 Vincent, Bory St., on bombs 190 Volcanic bombs 189 —— island in process of formation in the Atlantic 226 —— islands, their distribution 248 Wacke, its passage into lava 183, 257 Wackes, argillaceous 168, 178 Webster, Dr., on a basin-formed island 237 —— on gypsum at Ascension 201 White, Martin, on soundings 254 Wind, effects of, on the form of craters