Dikes, truncated, on central crateriform ridge of St. Helena. -at St. Helena; number of; coated by a glossy layer; uniform thickness of. -great parallel ones at St. Helena. -not observed at Ascension. -of tuff. -of trap in the plutonic series. -remnants of, extending far into the sea round St. Helena. Dislocations at Ascension. -at St. Helena. Distribution of volcanic islands. Dolomieu, on decomposed trachyte. -on laminated lava. -on obsidian. Dree, M., on crystals sinking in lava. Dufrenoy, M., on the composition of the surface of certain lava-streams. -on the inclination of tuff-strata. Eggs of birds embedded at St. Helena. -of turtle at Ascension. Ejected fragments at Ascension. -at the Galapagos archipelago. Elevation of St. Helena. -the Galapagos archipelago. -Van Diemen’s Land, Cape of Good Hope, New Zealand, Australia, and Chatham island. -of volcanic islands. Ellis, Rev. W., on ledges within the great crater at Hawaii. -on marine remains at Otaheite. Eruption, fissures of. Extinction of land-shells at St. Helena. Faraday, Mr., on the expulsion of carbonic acid gas. Feldspar, fusibility of. -in radiating crystals. -Labrador, ejected. Feldspathic lavas. -at St. Helena. -rock, alternating with obsidian. -lamination, and origin of. Fernando Noronha. Ferruginous superficial beds. Fibrous calcareous matter at St. Jago. Fissures of eruption. Fitton, Dr., on calcareous breccia. Flagstaff Hill, St. Helena. Fleurian de Bellevue on sphaerulites. Fluidity of lavas. Forbes, Professor, on the structure of glaciers. Fragments ejected at Ascension. -at the Galapagos archipelago. Freshwater Bay. Fuerteventura (Feurteventura), calcareous beds of. Galapagos archipelago. -parapets round craters. Gay Lussac, on the expulsion of carbonic acid gas. Glaciers, their structure. Glossiness of texture, origin of. Gneiss, derived from clay-slate. -with a great embedded fragment. Gneiss-granite, form of hills of. Good Hope, Cape of. Gorges, narrow, at St. Helena. Granite, junction with clay-slate, at the Cape of Good Hope. Granitic ejected fragments. Gravity, specific, of lavas. Gypsum, at Ascension. -in volcanic strata at St. Helena. -on surface of the ground at ditto. Hall, Sir J., on the expulsion of carbonic acid gas. Heat, action of, on calcareous matter. Hennah, Mr., on ashes at Ascension. Henslow, Prof., on chalcedony. Hoffmann, on decomposed trachyte. Holland, Dr., on Iceland. Horner, Mr., on a calcareo-animal substance. -on fusibility of feldspar. Hubbard, Dr., on dikes. Humboldt on ejected fragments. -on obsidian formations. -on parapets round craters. -on sphaerulites. Hutton on amygdaloids. Hyalite in decomposed trachyte. Iceland, stratification of the circumferential hills. Islands, volcanic, distribution of. -their elevation. Incrustation, on St. Paul’s rocks. Incrustations, calcareous, at Ascension. Jago, St. James island. Jasper, origin of. Jonnes, M. Moreau de, on craters affected by wind.