Page:Isaiah Bowman - Desert Trails of Atacama (1924).pdf/336

 Such a change in the position of the water supply of a ravine as Lange supposes in explanation of the habitability of El] Pucara, is exactly illustrated in the basin of Fiambalé, 200 miles west of this site. Penck has made important studies on the climate and relief of Fiambalé. He finds that the south- ward-flowing Rio Lajas at one time reached the town of Tinogasta (Fig. 1), whereas it now ends 5 kilometers (3 miles) farther north, where cultivated lands and a prosperous settle- ment were developed and were occupied until recent times, when the river ceased to flow beyond a point still farther north, leaving the cultivated lands desolate and the old settlements occupied only by shepherds that now camp there and get water by digging down two or three meters to the underflow.

The case of the Rio Lajas is an illustration of the same principle invoked by Lange. Penck further describes a highly important contrast in the positions of zones of moisture in the basin of Fiambala in northwestern Argentina (Fig. 87). Sum- mer pasture grows in a belt of mountain slope above 3500 meters, and there those Indians who follow the chase go in search of guanaco and vicufia. There are fresh green grass, springs, and brooks in every valley, in contrast to the great dryness of the basin, or bolsén, of FiambalA, where cactus and scrub predominate. The valleys are dry; and also in contrast to the relatively wet zone on the mountains is the dry and melancholy puna above the zone of grass in the alpine region. Such a zone of pasture and water supply is dependent upon the presence of a zone of cloud that forms in the high mountains and whose position is determined by the combina- tion of relief and winds already described (p. 273). If such a cloud zone were lowered or raised there would follow a cor- responding depression or elevation of the belt of pastures and woodland. Were there to be developed at any period a string of settlements, a civilization, buildings, cultivated lands, these would perforce change their situation to correspond with the change in rainfall and available water supply.

Whether such changes have been brought about in the period of Indian occupation, no one can yet say, but it cannot be too