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 scoriae.--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.