The zone of the elevated tablelands of the Andes without drainage toward the sea—the Puna—has still, below 22° S. latitude on the northern frontier of Argentina, a width of about 250 miles. This breadth steadily contracts southward as far as 28° S. latitude, where the Puna ends about the level of the road from Tinogasta to Copiapo.

To the east and south of the Puna the Argentine Andes are cut from north to south by a series of long gullies and large basins, between which there are lofty and massive chains with steep flanks. Some of these lie in the heart of the mountains, while others often open like gulfs upon the edge of the plain. These depressions with rectilinear contours are a common feature of the topography of the Andes in this latitude. The central plain of Chile is closely related to them. In the Argentine speech they are called valles: Valle de Lerma, Valle Calchaqui, Valle de Iglesias, de Calingasta, d'Uspallata. They are, however, not "valleys" in the sense of hollows made by erosion by running water. They owe their formation to tectonic movements, subsidences of the surface. The scanty rivers of the arid Anacs are not capable of doing work of that kind. When they enter the already formed bed of a valle, they seem to be lost in the immense space. Often they dry up in it, leaving behind the sediment and salts with which the water was laden. In other places they cut at right angles across the valle, escaping by narrow breaches in it, while the depression continues its course on either side, taking in sections of a number of independent streams.

Opposed to the valle is the eroded ravine, carved out by water, the quebrada. It opens upon a valle with a V-shaped mouth, which widens out at the top, and one can recognise at sight the various slopes and the successive stages of erosion. Narrow and winding, a level bed of shingle filling the entire base of the valley, it rises rapidly toward the mountains and provides a route from the valle to the puna. These valles, quebradas and puna are the three inhabited zones of the Andes. The first is the richest. The inhabitant of the valle, proud of his comparative comfort, has for his neighbour in the quebrada or the puna—the coyada—a contempt such as one finds the inhabitants of the good land in Europe feeling for the people in poorer districts.

The narrower the valle, the less rain there is. The observations give 112 millimetres of rain per year at Tinogasta, 290 at Andalgala, and 200 at Santa Maria. Salta and Jujuy have a much moister climate, and have no less than 570 and 740 millimetres of rain annually. This is because the eastern chain of the Andes, which stretches from the Sierra de Santa Victoria on the Bolivian frontier to Aconcagua, sinks lower at the latitude of Salta, and lets in the moisture of the Chaco to the heart of the zone of the Andes. The rains of Salta and Jujuy are suspended during the winter, but they are so heavy during the summer months (November to March) that maize, which needs only the summer rain, can be cultivated without irrigation. But when we follow the Valle de Lerma southward from Salta the maize harvest becomes more and more uncertain, and it is no longer sown in dry soil when we get to about twenty miles from Salta, in the latitude of the confluence of the Arias and the Juramento. However, the summer rains, which are good for maize, are very injurious to the vine; they spoil the grapes. Thus the southern limit of the cultivation of maize in dry soil almost coincides with the northern limit of the vine. At that point we have the real beginning of the typical scenery of the valles.

THE PATAGONIAN ANDES.

Mount Tronador (11,500 feet) on the Chilean frontier, dominating the road from Lake Nahuel Huapi to Chile. The glaciers still reach the bottom of the valley, which they filled at one time. A burnt forest in the foreground.

Plate III.

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