Chapter 5

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 been found.