Rocks of the lowest series.—A calcareous sedimentary deposit, with recent shells, altered by the contact of superincumbent lava, its horizontality and extent.—Subsequent volcanic eruptions, associated with calcareous matter in an earthy and fibrous form, and often enclosed within the separate cells of the scoriæ.—Ancient and obliterated orifices of eruption of small size.—Difficulty of tracing over a bare plain recent streams of lava.—Inland hills of more ancient volcanic rock.—Decomposed olivine in large masses.—Feldspathic rocks beneath the upper crystalline basaltic strata.—Uniform structure and form of the more ancient volcanic hills.—Form of the valleys near the coast.—Conglomerate now forming on the sea beach. Chapter II—FERNANDO NORONHA; TERCEIRA; TAHITI, ETC. FERNANDO NORONHA.—Precipitous hill of phonolite. TERCEIRA.—Trachytic rocks: their singular decomposition by steam of high temperature. TAHITI.—Passage from wacke into trap; singular volcanic rock with the vesicles half-filled with mesotype. MAURITIUS.—Proofs of its recent elevation.—Structure of its more ancient mountains; similarity with St. Jago. ST. PAUL’S ROCKS.—Not of volcanic origin.—Their singular mineralogical composition. Chapter III—ASCENSION. 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. Chapter 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. Chapter 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. Chapter VI—TRACHYTE AND BASALT.—DISTRIBUTION OF VOLCANIC ISLES.