Later the _valles_ were incorporated in the many variations of the historic high road, one of the first and busiest of Spanish America, which goes from the Rio de la Plata to Lima: a route both for armies and merchants. The plan proposed by Matienzo (1566) to make a road from the silver mines to the estuary of the Parana, through the Valle de Calchaqui, seems to have been intended merely to improve a line of communication that had already been in use. Buenos Aires for a long time received European goods by this road. About 1880 the Salta route recovered for a time its continental importance, during the Pacific War and the occupation by the Chileans of the maritime provinces of Bolivia.[20] At that time it was the only outlet for Bolivia. [20] See Brackebusch, "Viaje a la provincia de Jujuy," _Bol. Instit. Geog. Argent._, iv. 1883, pp. 9-17. [Illustration: VEGETATION OF THE INTERIOR VALLEYS (ANDES OF THE NORTH-WEST). _Descent of Tafi del Valle, going to Santa Maria. The ravine is excavated out of the mass of coarse deposits which forms a fringe between the mountain and the valley. On this permeable soil the vegetation is particularly thin. Cactus._ Photograph by the Author.] [Illustration: FOREST ON THE OUTER SLOPE OF THE SUB-ANDEAN CHAINS. _Sierra de San Antonio (Salta province). Perennial foliage, creepers, ferns._ Photograph by the Author. PLATE IV. To face p. 48.] But of all the forms of traffic that have enlivened the _valles_ the most constant, and the form that has had the most profound influence on their existence, is the movement of cattle. The cattle trade has been of fundamental importance in the history of the colonization of South America. Animals were the only goods that could be conveyed any great distance. At the beginning of the conquest the productive regions of the continent, which supplied the export trade with Europe, were very limited in extent. Pastoral colonization began at once, and spread over a very wide area. Herds of oxen, for meat or draught, horses, and mules, made their way toward the centres of consumption: towns like Lima, Bahia, and Rio, the Peruvian mines, and the sugar-refineries of the north-east of Brazil, and later toward the _yerbales_ of Paraguay or the seaports of the Caribs and the Rio Grande do Sul, where the jerked meat industry developed. The cattle routes converge upon these centres.