On the eastern slope of Aconcagua is the limit of the crescent of tropical forest, which begins about three thousand miles away, on the flank of the Venezuelan and Colombian Cordilleras, and is connected in the centre, in the equatorial zone, from Guaviare to Mamore, with the forests of the Amazon region. At its two ends it is reduced to a narrow belt which does not reach, in the east, the alluvial plains, the savannahs of the Orinoco and the scrub of the Chaco. The humid forest of the Argentine Andes is nowhere more luxuriant than near its southern limit, above Tucuman. There are no palms or tree-ferns, but the convolvulus abounds, and the evergreen trees are covered with epiphytes. Aconcagua is one of the sharpest climatological limits in the world. In the latitude of Salta one has only to go about 150 miles to pass from the moist forests of the sub-Andean chain of the Lumbrera to the arid valley of Cachi. On both sides of Aconcagua there are less than fifty-five miles between the sugar-cane fields won from the forest and the oasis of Andalgala, or that of Santa Maria, which are right in the desert zone. According as one approaches Aconcagua from the east or the west, one finds, from base to summit, either the successive stages of vegetation of the humid Andes--from forest to grain-sown prairie (_paramo_ or _pajonal_)--or those which are characteristic of the arid Andes, from the spiny scrub of the valleys to the fields of resinous _tola_ of the Puna. The contrast of climates is repeated in the character of the soils. Aconcagua contains in itself the entire Andes in miniature. At the foot of the narrow zone of Alpine crests, in the few square miles of the elevated valleys of Tafi and Pucara, there is a small agricultural and pastoral world, in a temperate climate, that has nothing quite like it elsewhere, narrowly confined between the forest and the desert.[32] [32] The higher valleys of Aconcagua offer inexhaustible interest to the visitor. At Sancho (Pucara valley) there is a group of Italian colonists who grow maize and wheat: a unique fact, I believe, in the whole of this part of Argentina. The Tafi valley is mainly pastoral, the pastures of the valley being used in summer and the forest for winter pasture.