Contenu du sommaire

Summary. — Southern Peru can be divided into 3 longitudinal zones : the coast range, high plains (about 3 000 ft) known as the Pampas, the main Sierra, gently sloping towards the aggradational Altiplano of lake Titicaca. Occasionally, the Pampas are separated from the Sierra by cristalline hills and intermediate brnins, the main one being the Arequipa trough, filled with a welded tuff, the sillar. The main chronological stages appear to be : — main uplift raising the late miocène Puna surface of erosion, cut in the Sierra, over the Pampas and Arequipa basin; an active volcanic period (chachani, then barroso) may have taken place after the uplift. The deposit of the sillar welded tuff is likely to have taken place during the chachani stage, which is about 3 million years old; — erosion in the Arequipa trough and correlative deposition of the glacis type alluvium of the Pampas; — joint uplift of all parts of the region (Coast range, Pampas, Arequipa basin, Sierra) in Pleistocene times, through a coastal warping or uplifting accounting for an uplift of about 3 000 ft.

Abstract. — As in the Alps, a « haute montagne » area may be found in the Atlantic mountains. Its rocky physical landscape, of glacial or periglacial origin, is a Pleistocene heritage now revealed by peat erosion. Its human landscape is a waste land of heaths and bogs, formerly devoted to summer transhumance, where forestry plantations are now encroaching; its lower part is the « hill pasture belt » of scattered and temporary settlement. Though beginning at low level and with hardly any frost and snow, the Atlantic « haute montagne » is the resuit of altitudinal change in the climate.