DEVELOPMENT IN THE SOUTH 149 



Part of the flocks which winter on the coastal plain pass 

 the summer in the south-west, on the high basaltic 

 tablelands of Somuncura. However, the whole of the 

 surface of the tableland cannot be used permanently, 

 or during the entire summer. There is plenty of water 

 in spring, when the snows have melted. In the middle 

 of the summer the flocks collect round the permanent 

 springs, and they scatter once more over the mountain 

 pastures during the autumn rains, before they return 

 to the plain. 



The second region is that of Valcheta. From 

 Aguada Cecilia to Corral Chico the railway follows 

 for sixty miles the edge of the outpour of lava from 

 the south, which covers the Tertiary clays. In front 

 of the basalt cliff the land dips in the north toward a 

 closed depression, the Bajo de Valcheta, the bottom 

 of which consists of clays impregnated with salt. Ter- 

 tiary marine strata surround this hollow in the west and 

 north, where they divide it from the Bajo del Gualicho, 

 but here they form only a thin skin which covers the 

 crystalline platform. The line of contact of the basalt 

 and the Tertiary marls is marked by a series of good 

 springs, and these give rise to permanent streams, 

 such as the Arroyo Valcheta and the Nahuel Niyeu. 

 At first they flow in a narrow valley crowned by basalts, 

 with peaty prairies at the bottom, then over Tertiary 

 marls, and, in the latitude of the railways, they pass 

 into a gorge cut through the granites before losing 

 themselves to the north in the salitral. A small agri- 

 cultural oasis is sustained by the waters of the Valcheta. 



The site of Valcheta has an exceptional importance 

 in the story of Patagonian colonization. It marks 

 a necessary stage in the Indian track from the Atlantic 

 to Nahuel Huapi, which is now followed by the line of 

 the railway. Musters halted there. The track from 

 Choele Choel, on the Rio Negro, to the southern coast 

 and the Santa Cruz also passed by there. It was so 

 much used, says Ezcurra, that the hoofs of the horses 



