One remarkable circumstance is the importance of the dunes in connection with the distribution of the underground water. The rain-water accumulates in the dunes and flows slowly through the sand to the sub-soil. The level of the underground sheet in the clay on which the dune rests is always nearer the surface in the neighbourhood of the dune. The dune itself has often a greener vegetation than the land around it. Nothing is more surprising than to find at Medanos (west of Bahia Blanca), in the middle of a plain of arid aspect, fields of lucerne and orchards lodged in the hollows of dunes that are still fresh. In the whole of the Buenos Aires province the dead district of the dunes is, on account of its water-supply, a good place for habitation. D'Azara notices the numerous water-spots which ran along the foot of the dead dunes of the Cerillada. All round were the white bones of the _baguales_. In the valleys of the central Pampa, where the sheet of water in the centre of the valley is often saline, the underground water improves gradually as one approaches the line of the dunes. Revolutions and wars interrupted the work of taming the cattle. When Galvez went from the Cordoba province to Buenos Aires at the end of the Rosas Government, he was struck by the condition of the ranches.[90] Many of them had been confiscated, or their owners driven into exile. Cattle were no longer marked, and they had become wild. The troubles of the emancipation-period were much less injurious to the Buenos Aires breeders than to those of Entre Rios. The Entre Rios herd was almost annihilated during the revolution, and some of the ranchers of the left bank crossed to the right bank of the Parana. After 1823 the pastoral wealth of Entre Rios was rapidly restored, thanks to raids on Brazilian territory. They were so profitable that the whole population took part in them. In 1827 the inhabitants of Bajada went there in such numbers that the town was half deserted. Every day thousands of cattle were collected on the bank of the Uruguay, and crossed the river. Some of them were even taken beyond the Parana, to the Santa Fe province. Woodbine Parish confirms this rapid restoration of Entre Rios, of which D'Orbigny was a witness. But this period of prosperity did not last long. The war with Uruguay, under Rosas, again ruined the Entre Rios ranches, and the drought of 1846 helped to scatter the remaining herds. Extensive breeding is only lightly rooted in the soil. The chief centres of production change their locality, as the political circumstances change, from one part of the Pampean plain to another. [90] V. Galvez, _Memorias de un viejo_ (Buenos Aires, 3 vols, in 16^{mo}, 4th ed, 1889).