In the rivers and lakes are found abundance of fish, tapirs, cavies, water-pigs, and other amphibious animals.
The great chain of the Andes, which borders and sends forth branches into Tucuman, is so high in some parts as to reach the regions of eternal snow; in it there are several mines, which were formerly worked by the Spaniards, and there remain striking vestiges of the mining operations carried on by the Peruvians.
The rivers of Tucuman are numerous, the principal ones being the Vermejo, the Salado, the Xuxuy, the Dulce and the Quarto. The Vermejo, or Rio Grande, rises near Casabinda, and flows with a stately stream into the La Plata, near Corrientes. The Salado takes its waters from many streams which flow down from the mountains of Tucuman, in south latitude 24°, and chiefly from those of the valley of Calchaqui, where it receives a large stream which comes from the south-west; it then runs into the valley of Huachipas, which name it takes, but soon changes it for that of Charomores, from a place so called; it then flows westward, and is called Pasage; as being in the road from Buenos Ayres to La Plata, it must be here crossed by travellers with some risk, owing to the rapidity of its current; it then is called De Balbuena, from passing through the settlement of that name, and is joined near this place by the Rio Piedras, and passes down through the district of Santiago del Estoro, from whence it runs eighty leagues, under the name of Salado, and loses itself eighty-six miles north-north-west of the city of Santa Fé, in a lake named El Mar Chiquito. The Chacos, or Dulce, runs by the side of this river, after it passes through Salta, and at last falls into it. Its whole course is 200 leagues, and it formerly reached Santa Fé, where it formed a peninsula with an arm of the La Plata, but having opened itself new channels by its great swellings, it now loses itself in the lake, which is the case with almost all the rivers of this province, as they generally form large sheets of water, from which they rarely issue.
The numerous lakes in this province are generally shallow, and produced by the overflowing of the rivers: but they have the singular quality of being mostly saline, particularly those in the neighbourhood of the Rio Vermejo.
There is in these vast plains through which the rivers pass an immense tract of land, the soil of which is saturated with fossil salt. It extends to the south of Buenos Ayres, and is about 700 miles in length by 150 in breadth. It is said that in this extent, which reaches to the Rio Vermejo, there is not a river, well or lake whose waters are not brackish. All the rivers which flow through it to the La Plata are fresh until they cross this waste, after which they become salt till they enter the great stream. Even the Pilcomayo and Vermejo, although they have a free course, have always a salt taste when the waters are low. This substance appears in the greatest abundance between Santa Fé and Cordova, and the salt quality of the soil reaches to St. Jago del Estero, where the whole ground is covered with a white incrustation even to the foot of the Cordillera.
Natural saltpetre is also collected in this part of the country, after a shower the ground being whitened with it. Chaco contains many salt lakes, and to the south-west of Buenos Ayres, they are found at from 400 to 450 miles distance. To these, journeys are frequently made with carts, in order to collect the fine crystallized grains which cover their banks.
The cattle of this country cannot subsist without this substance; they devour with avidity the salted clay they find in the ditches; and when this happens to fail, as is sometimes the case in Paraguay, they perish in the course of a short time.
From Buenos Ayres, the great road to Potosi and Lima passes through Tucuman. In 1748, regular stages were built all the way, post-houses were erected, and relays of horses and carriages provided.