Basaltic lavas.—Numerous craters truncated on the same side.—Singular structure of volcanic bombs.—Aeriform explosions.—Ejected granite fragments.—Trachytic rocks.—Singular veins.—Jasper, its manner of formation.—Concretions in pumiceous tuff.—Calcareous deposits and frondescent incrustations on the coast.—Remarkable laminated beds, alternating with, and passing into obsidian.—Origin of obsidian.— Lamination of volcanic rocks. IV.—ST. HELENA. Lavas of the feldspathic, basaltic, and submarine series.—Section of Flagstaff Hill and of the Barn.—Dikes.—Turk’s Cap and Prosperous Bays.— Basaltic ring.—Central crateriform ridge, with an internal ledge and a parapet.—Cones of phonolite.—Superficial beds of calcareous sandstone.— Extinct land-shells.—Beds of detritus.—Elevation of the land.— Denudation.—Craters of elevation. V.—GALAPAGOS ARCHIPELAGO. Chatham Island.—Craters composed of a peculiar kind of tuff.—Small basaltic craters, with hollows at their bases.—Albemarle Island; fluid lavas, their composition.—Craters of tuff; inclination of their exterior diverging strata, and structure of their interior converging strata.—James Island, segment of a small basaltic crater; fluidity and composition of its lava-streams, and of its ejected fragments.—Concluding remarks on the craters of tuff, and on the breached condition of their southern sides.— Mineralogical composition of the rocks of the archipelago.—Elevation of the land.—Direction of the fissures of eruption. VI.—TRACHYTE AND BASALT.—DISTRIBUTION OF VOLCANIC ISLES. The sinking of crystals in fluid lava.—Specific gravity of the constituent parts of trachyte and of basalt, and their consequent separation.— Obsidian.—Apparent non-separation of the elements of plutonic rocks.— Origin of trap-dikes in the plutonic series.—Distribution of volcanic islands; their prevalence in the great oceans.—They are generally arranged in lines.—The central volcanoes of Von Buch doubtful.—Volcanic islands bordering continents.—Antiquity of volcanic islands, and their elevation in mass.—Eruptions on parallel lines of fissure within the same geological period. VII.—AUSTRALIA; NEW ZEALAND; CAPE OF GOOD HOPE. New South Wales.—Sandstone formation.—Embedded pseudo-fragments of shale.—Stratification.—Current-cleavage.—Great valleys.—Van Diemen’s Land.—Palaeozoic formation.—Newer formation with volcanic rocks.— Travertin with leaves of extinct plants.—Elevation of the land.—New Zealand.—King George’s Sound.—Superficial ferruginous beds.—Superficial calcareous deposits, with casts of branches; its origin from drifted particles of shells and corals.—Their extent.—Cape of Good Hope.— Junction of the granite and clay-slate.—Sandstone formation. INDEX. GEOLOGICAL OBSERVATIONS ON VOLCANIC ISLANDS. CRITICAL INTRODUCTION.