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Urangan, 17 June, 2001
GEOLOGICAL OBSERVATIONS ON SOUTH AMERICA
by CHARLES DARWIN
Although in some respects more technical in their subjects and style than
Darwin's "Journal," the books here reprinted will never lose their value
and interest for the originality of the observations they contain. Many
parts of them are admirably adapted for giving an insight into problems
regarding the structure and changes of the earth's surface, and in fact
they form a charming introduction to physical geology and physiography in
their application to special domains. The books themselves cannot be
obtained for many times the price of the present volume, and both the
general reader, who desires to know more of Darwin's work, and the student
of geology, who naturally wishes to know how a master mind reasoned on most
important geological subjects, will be glad of the opportunity of
possessing them in a convenient and cheap form.
The three introductions, which my friend Professor Judd has kindly
furnished, give critical and historical information which makes this
edition of special value.
PLATE I. GEOLOGICAL SECTIONS THROUGH THE CORDILLERAS.
SECTION 1/1. SECTION OF THE PEUQUENES OR PORTILLO PASS OF THE CORDILLERA.
SECTION 1/2. SECTION OF THE CUMBRE OR USPALLATA PASS.
SECTION 1/3. SECTION OF THE VALLEY OF COPIAPO TO THE BASE OF THE MAIN
PLATE II. MAP OF SOUTHERN PORTION OF SOUTH AMERICA.
TABLE OF CONTENTS.
CHAPTER I.--ON THE ELEVATION OF THE EASTERN COAST OF SOUTH AMERICA.
Upraised shells of La Plata.--Bahia Blanca, Sand-dunes and Pumice-pebbles.-
-Step-formed plains of Patagonia, with upraised shells.--Terrace-bounded
valley of Santa Cruz, formerly a sea-strait.--Upraised shells of Tierra del
Fuego.--Length and breadth of the elevated area.--Equability of the
movements, as shown by the similar heights of the plains.--Slowness of the
elevatory process.--Mode of formation of the step-formed plains.--Summary.-
-Great shingle formation of Patagonia; its extent, origin, and
distribution.--Formation of sea-cliffs.
CHAPTER II.--ON THE ELEVATION OF THE WESTERN COAST OF SOUTH AMERICA.
Chonos Archipelago.--Chiloe, recent and gradual elevation of, traditions of
the inhabitants on this subject.--Concepcion, earthquake and elevation of.-
-VALPARAISO, great elevation of, upraised shells, earth or marine origin,
gradual rise of the land within the historical period.--COQUIMBO, elevation
of, in recent times; terraces of marine origin, their inclination, their
escarpments not horizontal.--Guasco, gravel terraces of.--Copiapo.--PERU.--
Upraised shells of Cobija, Iquique, and Arica.--Lima, shell-beds and sea-
beach on San Lorenzo.--Human remains, fossil earthenware, earthquake
debacle, recent subsidence.--On the decay of upraised shells.--General
CHAPTER III.--ON THE PLAINS AND VALLEYS OF CHILE:--SALIFEROUS SUPERFICIAL
Basin-like plains of Chile; their drainage, their marine origin.--Marks of
sea-action on the eastern flanks of the Cordillera.--Sloping terrace-like
fringes of stratified shingle within the valleys of the Cordillera; their
marine origin.--Boulders in the valley of Cachapual.--Horizontal elevation
of the Cordillera.--Formation of valleys.--Boulders moved by earthquake-
waves.--Saline superficial deposits.--Bed of nitrate of soda at Iquique.--
Saline incrustations.--Salt-lakes of La Plata and Patagonia; purity of the
salt; its origin.
CHAPTER IV.--ON THE FORMATIONS OF THE PAMPAS.
Mineralogical constitution.--Microscopical structure.--Buenos Ayres, shells
embedded in tosca-rock.--Buenos Ayres to the Colorado.--S. Ventana.--Bahia
Blanca; M. Hermoso, bones and infusoria of; P. Alta, shells, bones, and
infusoria of; co-existence of the recent shells and extinct mammifers.--
Buenos Ayres to St. Fe.--Skeletons of Mastodon.--Infusoria.--Inferior
marine tertiary strata, their age.--Horse's tooth. BANDA ORIENTAL.--
Superficial Pampean formation.--Inferior tertiary strata, variation of,
connected with volcanic action; Macrauchenia Patachonica at S. Julian in
Patagonia, age of, subsequent to living mollusca and to the erratic block
period. SUMMARY.--Area of Pampean formation.--Theories of origin.--Source
of sediment.--Estuary origin.--Contemporaneous with existing mollusca.--
Relations to underlying tertiary strata. Ancient deposit of estuary
origin.--Elevation and successive deposition of the Pampean formation.--
Number and state of the remains of mammifers; their habitation, food,
extinction, and range.--Conclusion.--Supplement on the thickness of the
Pampean formation.--Localities in Pampas at which mammiferous remains have
CHAPTER V.--ON THE OLDER TERTIARY FORMATIONS OF PATAGONIA AND CHILE.
Rio Negro.--S. Josef.--Port Desire, white pumiceous mudstone with
infusoria.--Port S. Julian.--Santa Cruz, basaltic lava of.--P. Gallegos.--
Eastern Tierra del Fuego; leaves of extinct beech-trees.--Summary on the
Patagonian tertiary formations.--Tertiary formations of the Western Coast.-
-Chonos and Chiloe groups, volcanic rocks of.--Concepcion.--Navidad.--
Coquimbo.--Summary.--Age of the tertiary formations.--Lines of elevation.--
Silicified wood.--Comparative ranges of the extinct and living mollusca on
the West Coast of S. America.--Climate of the tertiary period.--On the
causes of the absence of recent conchiferous deposits on the coasts of
South America.--On the contemporaneous deposition and preservation of
CHAPTER VI.--PLUTONIC AND METAMORPHIC ROCKS:--CLEAVAGE AND FOLIATION.
Brazil, Bahia, gneiss with disjointed metamorphosed dikes.--Strike of
foliation.--Rio de Janeiro, gneiss-granite, embedded fragment in,
decomposition of.--La Plata, metamorphic and old volcanic rocks of.--S.
Ventana.--Claystone porphyry formation of Patagonia; singular metamorphic
rocks; pseudo-dikes.--Falkland Islands, palaeozoic fossils of.--Tierra del
Fuego, clay-slate formation, cretaceous fossils of; cleavage and foliation;
form of land.--Chonos Archipelago, mica-schists, foliation disturbed by
granitic axis; dikes.--Chiloe.--Concepcion, dikes, successive formation
of.--Central and Northern Chile.--Concluding remarks on cleavage and
foliation.--Their close analogy and similar origin.--Stratification of
metamorphic schists.--Foliation of intrusive rocks.--Relation of cleavage
and foliation to the lines of tension during metamorphosis.
CHAPTER VII.--CENTRAL CHILE:--STRUCTURE OF THE CORDILLERA.
Central Chile.--Basal formations of the Cordillera.--Origin of the
porphyritic clay-stone conglomerate.--Andesite.--Volcanic rocks.--Section
of the Cordillera by the Peuquenes or Portillo Pass.--Great gypseous
formation.--Peuquenes line; thickness of strata, fossils of.--Portillo
line.--Conglomerate, orthitic granite, mica-schist, volcanic rocks of.--
Concluding remarks on the denudation and elevation of the Portillo line.--
Section by the Cumbre, or Uspallata Pass.--Porphyries.--Gypseous strata.--
Section near the Puente del Inca; fossils of.--Great subsidence.--Intrusive
porphyries.--Plain of Uspallata.--Section of the Uspallata chain.--
Structure and nature of the strata.--Silicified vertical trees.--Great
subsidence.--Granitic rocks of axis.--Concluding remarks on the Uspallata
range; origin subsequent to that of the main Cordillera; two periods of
subsidence; comparison with the Portillo chain.
CHAPTER VIII.--NORTHERN CHILE.--CONCLUSION.
Section from Illapel to Combarbala; gypseous formation with silicified
wood.--Panuncillo.--Coquimbo; mines of Arqueros; section up valley;
fossils.--Guasco, fossils of.--Copiapo, section up valley; Las Amolanas,
silicified wood.--Conglomerates, nature of former land, fossils, thickness
of strata, great subsidence.--Valley of Despoblado, fossils, tufaceous
deposit, complicated dislocations of.--Relations between ancient orifices
of eruption and subsequent axes of injection.--Iquique, Peru, fossils of,
salt-deposits.--Metalliferous veins.--Summary on the porphyritic
conglomerate and gypseous formations.--Great subsidence with partial
elevations during the cretaceo-oolitic period.--On the elevation and
structure of the Cordillera.--Recapitulation on the tertiary series.--
Relation between movements of subsidence and volcanic action.--Pampean
formation.--Recent elevatory movements.--Long-continued volcanic action in