354 AMAZONIA AND LA PLATA. 



Interrapled southwards by tlie deep gorge of the Rio de las Burras the 

 plateau falls to less than 13,000 feet, but farther on again rises to great altitudes 

 in the Nerados or snowy crests of Pasto Grande, Acay, Cachi, and others. Even 

 farther east, the plateau, although deeply ravined and carved into promontories 

 and isolated ridges, still presents several summits over 10,ôOO feet high, and snow- 

 clad for a part of the year. In the sierra which skirts the west side of the Jujuy 

 vallev the JSTevado de Chaniand the Très Cruces attain an elevation of over 18,000 

 feet. North of Jujuy the Zenta range, projecting like a long promontory beyond 

 the plateau, is crossed at the Zenta pass by the route from Oran to Humahuaca at 

 an elevation of 14,780 feet, while other summits in the same range rise to 16,400 

 feet. Yet the snow^ which sometimes falls melts almost immediately. In this dry 

 climate, and under this latitude (24° S.), the lower limit of the snow line would pro- 

 bably lie between 18,000 and 20,000 feet. 



All these highlands and plateau escarpments preserve traces of the ice-cap which 

 formerly descended far into the plains. The whole region had certainly its glacial 

 epoch, perhaps, even successive periods of glaciation. Everywhere the foot of 

 the mountains is flanked by terraces a few hundred yards high, Avhere gravels are 

 intermingled with layers of sand. These and other analogous phenomena can 

 scarcely be explained by the simple action of water and the deposit of alluvial 

 matter. 



ACONQUIJA AXD FaMATIXA UpLAXDS. 



West of Salta the chain of mountains skirting the plateau recedes continually 

 westwards, diminishing in breadth as well as in height in the direction of the south. 

 Here the system has been deeply scored by running waters. One lofty ridge has 

 even been completely detached from the Andean uplands by arid spaces, gradually 

 worn down to their present level by glaciation and erosion. The Sierra d'Acon- 

 quija, as this isolated range is called, stretches in a sinuous line from north to 

 south, west of the Tucuman plains. Including its extreme offshoots it has a total 

 length of no less than 280 miles between the great bend of the Juramento and the 

 headwaters of the Rioja. But the Aconquija proper, which is disposed in the 

 direction from north-east to south-west, is scarcely more than 30 miles long. It 

 falls very abruptly on its west side facing the Andes, but slopes more gently east- 

 wards, where it is flanked by foothills which are wooded here and there. Erora the 

 Clavijo, as the central mass is called, the spurs branch off in various directions — 

 in the north, the Cumbres de Calchaqui ; in the west, the Sierra del Atajo ; in the 

 south, the Ambato range; in the south-east, the Altos, continued by the Ancaste 

 mountains. In the winter of 1893, the geologist, Rodolfo Ilauthal, scaled for the 

 first time the culminating peak of the Aconquija system, which he calculated to be 

 17,720 feet high. Before attacking the dominating cone he had passed two days 

 at an altitude of 14,760 feet, in a fissure of the rocks under shelter from a furious 

 gale. Although situated in the temperate zone, Aconquija has no glaciers, though 

 clear traces survive of former crystalline streams. At a height of lr5,420 feet, 



