The business done in the fairs of the southern Andes is very varied in character, but their main function was always as markets for stock.[29] They are held in March or April, when the rains do not fall, but pasture is still abundant and travelling easy. The fair at Vilque, north of Lake Titicaca, is no longer visited by dealers in Argentine mules. The Salta fair which was held at Sumala, near Rosario de Lerma, has ceased to be important; at the close of the eighteenth century it was the chief centre of the mule-trade. The fair held at Jujuy is still, like the annual pilgrimage to the Virgen del Valle de Catamarca, one of the great dates in the life of the Andes. In the eighteenth century it was mainly a cattle-fair, but it is now frequented only by mule-dealers. The development of the railways is gradually causing it to decline. [29] There is an interesting study of fairs on the elevated tableland by G. M. Wrigley, "Fairs of the Central Andes," in the _Geographical Review_ (New York), vii. 1919, pp. 65-80. The cattle-trade has long been really a form of barter. The Argentinians who took their herds to Peru brought back with them European goods that had come via Panama and the Pacific. At Jachal direct communication with Argentina is still so costly that they prefer to get many manufactured articles from Chile. Everywhere else, however, the sellers of stock take payment in cash. The Santa Marienos bring back from Bolivia only a few bags of coca and, for chief payment, letters of exchange, which they cash in the Salta banks when they return. Their gains swell the profits of the merchants of Salta, Catamarca, and Jujuy, who get their goods at the large importing houses of Buenos Aires. It is the first form under which the influence of Buenos Aires reaches the _valles_. It gets their custom before it begins to absorb their produce. A large proportion of the stock sent to Chile now comes from the Andean valleys themselves. The most arid and desolate regions round the oases breed only goats and asses; but as soon as the soil improves sufficiently to give a better vegetation, it is found good enough for a hardy and tenacious breed of horned cattle. The land is divided into large ranches, and the owners have also lucerne-farms, either individually or communally, the tillers of the oasis each putting in their beasts, which wander about in small groups without control. During the summer they go of their own accord up to the _cerros_, where the rains have brought out the vegetation, and drinking-water is found in the ravines for several months. In the winter they return to the valley, within range of the reservoirs and permanent _acequias_. Bodenbender gives us a few details about movements from place to place owing to such differences, as they are in vogue in the western part of the province of La Rioja, in the district of Guandacol. There the herds are taken during years of drought up to the mountains of the west.