The mountain of _Duida_ is the highest point which has yet been seen of the Cordillera of the Cataracts; this volcano has not hitherto been explored, but its height has been found to be 8465 feet above the sea. The Cordillera of the Cataracts is remarkable for the abrupt descent of its southern face. It is said to exhibit no rock of secondary formation, or to contain any petrifactions or organic remains, consisting only of granite, gneiss, mica, slate, and hornblende; this however applies only to the part visited by M. de Humboldt, from the Rio Negro to the frontier of the Grand Para, a distance of 600 miles. The third great branch from the main body of the Andes, is that of _Chiquitos_, between the 15th and 20th degree of south latitude, which, sweeping from the main chain in a semicircular shape, traverses the province of the same name, connecting the heights of Paraguay and La Plata with those of Chili and Peru. The great rivers which fall into, and form parts of the La Plata and the Maranon, rise in this branch, but as no satisfactory accounts of it have been published, it is impracticable to give any general description of its particular properties and forms. These branches form three immense plains between their bases, open to the southern Atlantic Ocean on the east, and shut out from the Pacific by the great trunk of the Andes on the west; the most northerly is the _Savannah_, or _Plain of the Orinoco_, noted for its luxuriant herbage, and possessing only a few scattered trees. _The plain of the Amazons_, or _Maranon_, succeeds to that of the Orinoco on the opposite side of the central branch. On this widely extended tract, forests, coeval with the soil they are nourished by, extend their gloomy and nearly impenetrable fastnesses, inhabited only by tribes of savage and wandering Indians, whose ferocity allies them to the beasts of prey which roam in every part of the savannahs of the Maranon. The third great plain is that distinguished by the appellation of _the Pampas_, or _the Plains of the La Plata_, resembling in some measure the valley of the Orinoco, being covered with a strong and luxuriant growth of herbage, and occupied by countless herds of wild cattle, which are hunted solely for the sake of their hides, these forming one of the chief articles of the export trade of the viceroyalty of Buenos Ayres.