The fields do not cover the whole area of the annual inundations. They are confined to the part where the flood is fertilizing; where it leaves behind it a fine, useful clay which keeps the store of moisture for several months. In other places the current is too rapid. It furrows the soil, leaves large holes in it like the _lones_ in the flood-area of the Rhone, and sweeps away the barriers; or the water brings sterile sand which it deposits in long stretches; or again, if it is not drained away in time and evaporates on the spot, it deposits the salts it contains, and the land, looking as if it had a white leprosy, becomes unfit for vegetation. The floods begin in summer, during November or December. They are caused by the rain-storms in the Tucuman district, and are very irregular. Some of the houses are evacuated, and others are protected by walls of earth, which are raised from hour to hour according to the rise of the waters. Behind these walls the people await the abatement of the flood. When the mud which is left behind has the proper consistency, they till it and sow wheat. The wheat grows in the winter, and is harvested in November quickly, so that the fresh flood may not overtake it. The caprices of the flood compel them frequently to change the sites of their houses and fields. The ancient village of Loreto was evacuated after a flood, and is now merely a mass of deserted ruins. Round the naked trunks of the _algarrobas_, killed by excessive deposits of sand or salt, are uniform colonies of plants of the same age and the same species, which invade the area where the adult scrub has been destroyed. The mill has been rebuilt less than a mile away, and has not lost its customers, who have raised their _ranchos_ some distance away. The insecurity of the plots has prevented the development of small ownership. The farmers are tenants of the ranches, which stretch from the river to a considerable distance in the interior.