VOLCANIC ISLANDS.


TABLE OF CONTENTS.


CRITICAL INTRODUCTION.


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 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.


CHAPTER II.--FERNANDO NORONHA; TERCEIRA; TAHITI, ETC.

FERNANDO NORONHA.--Precipitous hill of phonolite.

TERCEIRA.--Trachytic rocks: their singular decomposition by steam of high
temperature.