Chapter I—St. Jago, in the Cape De Verde Archipelago.

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.