The River _Ica_, or _Putamayo_, rising in the district of Ibarra, falls into the Maranon, east of the Napo, after a course of 300 leagues. The _Yapura_, which rising in Popayan, under the name of _Caqueta_, runs into the Maranon, by several mouths. One branch of this river was formerly thought to be the great Rio Negro, the junction of which, with the Orinoco, is so exactly laid down in a map of Father Ferreira, of the city of Gran Para, that it differs in very few respects from the late discoveries of M. de Humboldt on the Cassiquiare. The Portuguese penetrated from the Amazons to the Orinoco, by means of canoes, as early as 1774; and M. de la Condamine, also gives a very reasonable description of this famous junction. The _Rio Negro_ rises a short space north of the Caqueta or Yapura, and after an amazing course, sends off one branch to the Orinoco, directly north, and another south-easterly to the Maranon. The northern branch is now known by the name of the _Cassiquiare_: these afford an inland communication between two of the most celebrated rivers in the world; and as the settlements of the Spaniards in Caraccas, and the Portuguese in Guiana, approach each nearer and nearer every year, this natural canal will shortly become of great importance. The most remarkable natural curiosity in Maynas is the Pongo or straight, through which the Lauricocha passes the Andes. The river above the Pongo, runs down a mountain channel, forming rapids, cataracts, &c., approaching the eastern ridge of the Andes, where it suddenly contracts its bounds, from 1600 to 600 feet, and rushes through a crevice of tremendous height for the space of eight miles. The vortices are so powerful here, that a missionary was kept in one for two days, and would have perished with his raft, if the river had not suddenly swollen and carried him out of it. Balsas are always used in this strait, as the spring they have resists the shocks which they experience when dashed against the rocks; in such cases, a canoe or boat would be broke to pieces. La Condamine was carried through on his balsa at the rate of nine miles an hour, and emerging from the jaws of the mountain, he found himself in a new world, separated from all human intercourse, on a fresh water sea, surrounded by a maze of rivers and lakes, which struck in every direction into the gloom of an immense forest, impenetrable but for them. New plants and animals were exhibited to his view, the soil covered with a dense mass of vegetation never appeared, and nothing was to be seen but verdure and water. Below Borja, and four or 500 hundred leagues beyond it a stone or a pebble is as rare as a diamond.