The navigation of the Parana is one of the chief sources of the prosperity of Buenos Aires. Even if the development of the import trade at Rosario or Santa Fe is partly at the expense of the capital, and the boats laden with cereals do not stop at its quays, still the coasting traffic on the river is in great part meant for Buenos Aires. In returning, rather than go empty, the boats take cargoes of European products bought from the Buenos Aires importers. By means of the Parana the import-trade sphere of influence of Buenos Aires reaches beyond the frontiers of Argentina, as far as Paraguay and part of Brazil. Buenos Aires is, moreover, the main centre for equipping the steamboats of the river. Its capital dominates the Parana. Lastly, the Parana supplies it with an export freight which must not be overlooked. It is at Buenos Aires that the hides, tobacco and timber and extracts of _quebracho_ for oversea markets, shipped on schooners in the upper reaches of the river which are impassable for steamers, are trans-shipped for abroad. CHAPTER IX THE POPULATION The distribution of the population--The streams of emigration to the interior--Seasonal migrations--The historic towns--The towns of the Pampean region--Buenos Aires. A large-scale chart of the mean density of the population for each province--like those which were published in the latest Argentine Census-reports--has no geographical value for the west and north-west, where oases of slight extent are separated by vast desolate stretches, deserted because of the lack of water. In the Pampean region, on the other hand, the population is distributed in a very regular manner, and the mean densities calculated fairly represent the facts. To the several types of exploitation, of which we have studied the distribution on the Pampa, there correspond unequal densities of population. Cattle-breeding, for instance, requires only a thin population. The early pastoral colonization of the plain on the west of the Salado was carried out, between 1880 and 1890, with a very small number of workers. A large ranch of 400 square kilometres on the northern edge of the Pampa (the Tostado ranch) only employs about a hundred men, or one for four square kilometres. The density increases appreciably for sheep-breeding on the _pastos tiernos_ of Buenos Aires province, where a ranch of a hundred square kilometres, devoted to producing wool, with fifty or sixty shepherds, sustains at least 200 persons, or two to the square kilometre.[136] The density is not appreciably greater in the area of wheat-growing on a large scale, where the extent cultivated by one family reaches, including fallow, 200 hectares. But it may, even apart from the urban population, be more than ten to the square kilometre in the maize belt. [136] The density is twenty times less in the ranches which use the meagre pastures of the Rio Negro.