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 sedimentary formations.

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.


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.


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 the Cordillera.--Conclusion.


Charles Darwin

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Observations Geologiques sur les Iles Volcaniques
Voyage of the Beagle