The great industrial forms of cultivation, the sugar-cane and the vine, gave a new aspect to the scenery of Tucuman and Mendoza at the end of the nineteenth century. The increase of population and wealth which they entailed was so sudden, the economic advance so swift, that the owners of vineyards and the sugar-makers have now lost all recollection of the primitive industries which gave life to colonial Tucuman and Mendoza, and were maintained until the last generation. Nevertheless, if one compares Tucuman or Mendoza with some centre of irrigated tillage in north-west Argentina, one quickly perceives the original features which three centuries of history have given them. The system of land-tenure, water-rights, the distribution of the cultivated zones, and a thousand other features, show that the colonization is old. The exploitation of the soil and utilization of the water have not proceeded on a methodical plan, conceived in advance, which would make each piece of work--the dams and channels of distribution, for instance--subordinate to the whole. The engineers who constructed the great modern dams of Mendoza, San Juan and Sali, had not to create a region of new estates, but merely to improve the water-supply, which was used wastefully by the existing estates. There is nothing more suggestive than the contrast between these stone dams, built according to all the rules of hydraulics, and the network of irregular channels, following the accidental variations of the land and the slope, which preceded them, and to which they have been accommodated as far as possible. In some cases the primitive _acequias_ could not be altered so as to start from the dam. The accumulations of water succeed each other down the slope, held up by a simple barrier of branches and earth which is periodically destroyed by floods. The modern flood-proof dam (_dique nivelador_), which cuts the torrent in its entire width, and enables them to make use of its whole volume, allows a certain amount of water to pass, for the use of the _acequias_ lower down. This falls back into the broad, stony bed, exposed to evaporation and infiltration as it was before. * * * * *