THE PHYSICAL SETTING OF THE CHILEAN BORATE 
DEPOSITS 
ROLLIN T. CHAMBERLIN 
The University of Chicago 
North of the Tropic of Capricorn, the Andes of Chile and 
Bolivia stand forth as two massive chains with a lofty plateau 
between. The two great ranges of Andes are known as the Cor- 
dillera Occidental and the Cordillera Oriental, or Cordillera Real. 
The lofty tableland between passes under the name of Altaplanicie, 
or Great Central Plateau of Bolivia. It is in some respects one 
of the most remarkable topographic features of South America. 
Throughout nearly ten degrees of latitude its surface maintains 
an elevation of approximately 12,000-13,000 feet above sea-level. 
But apart from its greater elevation this broad inter-Andine table- 
land shows a resemblance to portions of the great basin region in 
the western United States. 
This plateau is boxed in on the east by the great wall-like 
ridge of the Eastern Cordillera which culminates in the giant peaks 
of Illimani (21,200 feet) and Illampu (21,490 feet). On the west 
the plateau is bounded by a remarkable string of volcanoes which 
constitute the Western Cordillera. The two systems of mountains 
are totally unlike. While the eastern range, or Cordillera Real, 
is composed of folded Paleozoics, with the still older granites and 
gneisses exposed in the axis of the range, the Western Cordillera 
is conspicuous chiefly as a chain of volcanic cones perched upon 
the western edge of the great plateau. These volcanic cones rest 
upon folded Mesozoic strata, chiefly of Jurassic and Cretaceous 
age. The body of the plateau itself is composed principally of 
beds ranging in age from the Devonian to the Cretaceous. 
Throughout the extent of the plateau, in Chile, Bolivia, aud 
Peru, are numerous lakes, saline marshes, and beds of former 
lakes, most of which possess no outward drainage. The large 
bodies of water which still persist, like Lake Titicaca and Lake 
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