Once in the Paraguay, the main object of the voyage was accomplished. Unfortunately, however, for the adventurers themselves, they were there seized upon by Dr. Francia, the despotic ruler of that country, who, worse than the savages, detained them for five years.[51] He also deprived them of their papers; and thus the details of a most interesting voyage were lost, although the great and highly important fact was established beyond dispute of the existence of a safe and navigable water-communication the whole way from Oran to Buenos Ayres; a result which must sooner or later be of immense consequence to the inhabitants of the Upper Provinces.
About thirty miles below the mouth of the Vermejo the Paraguay is joined from the east by the great river Paranã, which name it thence takes till it is finally lost in the Rio de la Plata. This river, rivalling in extent the Paraguay itself, rises in the mountain-chains to the north-west of Rio de Janeiro, in latitude 21°. Turning first westward, and afterwards towards the south, it is increased by several large rivers, amongst which the most noted are the Paranaiba, the Tieté, the Paranapané, and the Curitava. On reaching the Guarani Missions, near Candelaria, in about lat. 27° 30´, it turns again westward, and runs with little deviation from that parallel till it falls into the Paraguay. Thence these two mighty rivers, mingling their waters flow on in one vast and uninterrupted stream, gradually increased by many rivers of minor importance, which join it from either side, till they finally empty themselves through a well-defined delta into the estuary of La Plata.
The extent of the practicable navigation on the two great branches of this mighty river varies with the geological formation of the countries through which they respectively pass.
The Paranã, whilst running through the mountainous districts of Brazil, is broken by many falls above the Guarani Missions, especially one called the Salto Grande, in lat. 24° 4´ 58" (as fixed by the officers of the Boundary Commission in 1788), where the river, which immediately before is nearly a league across, becomes suddenly confined by a rocky pass not more than sixty yards in width, through which it rushes with inconceivable fury, and forms a splendid cataract, between 50 and 60 feet high, dashing down with such thundering noise that it is said to be heard at a distance of five or six leagues. For a hundred miles afterwards, as far as the mouth of the river Curitiba, in lat. 25° 41´, the river is nothing but a succession of falls and rapids.