L. AGASSIZ. Footnote 92: Humboldt’s Personal Narrative, Bohn’s Scientific Library, Vol. II. Chap. XX. p. 267. Footnote 93: The Emperor had written to Mr. Agassiz that, during the time when he took command of the Brazilian army on the Rio Grande, he had caused collections of fishes to be made for him from several of the southern rivers. Footnote 94: To-day I cannot give a more precise account of the final result of my survey. Though all my collections are safely stored in the Museum, every practical zoölogist understands that a critical examination of more than eighty thousand specimens cannot be made in less than several years.—L. A. Footnote 95: The rest of this letter is omitted, as its substance is contained in Chapter XIII., on the Physical History of the Amazons. CHAPTER XIII. PHYSICAL HISTORY OF THE AMAZONS. DRIFT ABOUT RIO DE JANEIRO.—DECOMPOSITION OF UNDERLYING ROCK.—DIFFERENT ASPECT OF GLACIAL PHENOMENA IN DIFFERENT CONTINENTS.—FERTILITY OF THE DRIFT.—GEOLOGICAL OBSERVATIONS OF MESSRS. HARTT AND ST. JOHN.—CORRESPONDENCE OF DEPOSITS ALONG THE COAST WITH THOSE OF RIO AND THOSE OF THE VALLEY OF THE AMAZONS.—PRIMITIVE FORMATION OF THE VALLEY.—FIRST KNOWN CHAPTER OF ITS HISTORY.—CRETACEOUS FOSSIL FISHES.—FORMER EXTENT OF THE SOUTH-AMERICAN COAST.—CRETACEOUS FOSSILS FROM THE RIO PURUS.—COMPARISON BETWEEN NORTH AND SOUTH AMERICA.—GEOLOGICAL FORMATIONS ALONG THE BANKS OF THE AMAZONS.—FOSSIL LEAVES.—CLAYS AND SANDSTONES.—HILLS OF ALMEYRIM.—MONTE ALÉGRE.—SITUATION AND SCENERY.—SERRA ERERÉ.—COMPARISON WITH SWISS SCENERY.—BOULDERS OF ERERÉ.—ANCIENT THICKNESS OF AMAZONIAN DEPOSITS.—DIFFERENCE BETWEEN DRIFT OF THE AMAZONS AND THAT OF RIO.—INFERENCES DRAWN FROM THE PRESENT CONDITION OF THE DEPOSITS.—IMMENSE EXTENT OF SANDSTONE FORMATION.—NATURE AND ORIGIN OF THESE DEPOSITS.—REFERRED TO THE ICE-PERIOD.—ABSENCE OF GLACIAL MARKS.—GLACIAL EVIDENCE OF ANOTHER KIND.—CHANGES IN THE OUTLINE OF THE SOUTH-AMERICAN COAST.—SOURÉ.—IGARAPÉ GRANDE.—VIGIA.—BAY OF BRAGANZA.—ANTICIPATION.