The river Cassiquiari, long conjectured to be a strong branch of the Orinoco, but now known to be an arm of the Negro, communicates also with the Amazons, its streams having been visited by M. de Humboldt, who encountered great perils in the undertaking, by the force of the current and other obstacles. The whole country for 300 miles was a complete desert, in which the ants and mosquitoes were so exceedingly troublesome as almost to deter the traveller from proceeding. He entered the Orinoco, by the Cassiquiari in 3° 30' north-latitude, and mounted the current of the great river as far as Esmeraldas, the last Spanish settlement in that quarter. The mouths of the Orinoco are very dangerous to navigators; the largest is six leagues in width, and seven of them are navigable for large vessels. The isles formed by these are of very great extent, and are inhabited by the _Guaraounos_ and _Mariusos_ Indians. On the banks of the Orinoco the magnificence of the scenery is beyond description. Forests of the greatest extent are filled with aromatic trees, which diffuse the most delightful odour; birds of every singular variety of beautiful plumage are everywhere observed, and hordes of monkeys follow the astonished traveller. Passing these forests, enormous plains extend their verdant surfaces further than the eye can reach, and the cataracts of the Orinoco give their name to the whole Cordillera, and are represented to be the most tremendous that have ever been observed; but no good description of these falls has yet been given, though they constitute the only outlets from the country situated on the east of the Andes to the vast plains of the Maranon. These cataracts are at Maypura and Atures, two villages in about 6° north-latitude, near the great bend of the river. The periodical inundation of the Orinoco begins in April and ceases in August; in October the flood is low, arriving at its shallowest point in February; the rise is equal to thirteen fathoms at the distance of ninety leagues from the ocean. The mouth of the great estuary is in 8° 30' north-latitude, and 59° 50' west longitude. The caymans, or alligators, are very numerous, and very formidable throughout its whole length, which may be estimated at about 1250 miles.