[Illustration: THE PAMPEAN PLAIN. THE RIO BAMBA (IN THE SOUTH OF THE CORDOBA PROVINCE, 500 FEET ABOVE SEA-LEVEL). _Small circular lagoons. The underground water, which comes from the Sierras to the north-west, here reaches the surface. Zone of lucerne farms._ Photograph by the Author.] [Illustration: THE PAMPEAN PLAIN. BUENA ESPERANZA (SAN LUIS PROVINCE, 1,166 FEET ELEVATION). _The plain is sown with quick and dead dunes, often shaped in a circle round a lagoon. A dune invaded by vegetation._ Photograph by the Author. PLATE XVI. To face p. 182.] Primitive breeding affords few examples of periodical migration for the better use of pasturage. In 1822, in the course of a journey amongst the Sierras de Tandil and de la Ventana, Colonel Garcia noticed that the Indians kept their cattle round the temporary lagoons of the plain in the winter, and went up to the mountain-streams in summer. Transhumation movements of this kind were difficult for the creole ranchers, whose fairly large herds could not be handled easily. The Chascomus breeders, however, at the close of the eighteenth century, drove their cattle to the low banks of the Salado during the dry season.[91] Garcia also notices the importance of the Salado pastures for the ranches of Salto, Areco, and Lujan.[92] The need to remove the herds in the dry season, and to find _invernadas_ within reach of the former ranches, was due to the change brought about in the natural vegetation of the Pampa and the spread of the _pasto dulce_. The annual herbs which compose the _pasto dulce_ die and disappear after fertilization. Until the autumn rain they leave the ground quite naked, whereas the tough grasses of the _pasto duro_ afforded a thin but permanent pasture. [91] _Diario de un reconocimiento de las guardias y fortines que garnecen la linea de frontera de Buenos Aires_ (1796), by D. Felix de Azara (Coll. de Angelis, vi.). [92] _Nueva plan de fronteras de la Provincia de Buenos Aires por el Colonel Garcia_ (1816, Coll. de Angelis, vi.). * * * * *