PHYSICAL FEATURES AND GENERAL GEOLOGY. 
Physically, Colombia may be divided into two regions, the East- 
ern Plains or Llanos of the Orinoco, and the Western mountains. 
The Andes, entering Colombia from the south, divide into three 
approximately parallel chains, the Eastern, Central and Western 
’ Cordilleras. These are sometimes known as the Szerra del Choco, 
Sterra del Quindiu and the Sterra del Suma Paz, respectively. They 
are separated by the deep, longitudinal valleys of the Cauca and the 
Magdalena, the important waterways.of the republic. It is in these 
three chains that the ores occur. The Western and Central Cordil- 
leras are much richer than the Eastern. Besides these three ranges 
there is in the North the great massif of Santa Marta, which Reclus 
considered to be not a part of the Andean system. On the North 
and West a chain of the Andes enters the Isthmus of Darien from 
Central America‘and dies out in hills on the northwest coast. In this 
region it is separated from the Cordillera Occidentale (the Western 
Cordillera) by the Atrato Valley. In this chain there were formerly 
many mines, one of which, the Espiritu Santo, has been reopened 
recently. In the past, mines were worked in many parts of the coun- 
try as placers are at present. In 1892, when this collection was 
made, mines in operation existed with but few exceptions only in the 
two mountain Departments of Antioquia and Tolima. The great 
valleys of the Atrato, the Cauca, and the Magdalena, are very deep, so 
that strips of tropical climate extend much farther into the mountains 
than the map suggests. Even in the mountainous state of Antioquia, 
mining districts have been deserted on account of the hot, dangerous 
climate. On the other hand, the peaks and ridges are placed upon 
broad bases, so that, excluding the Llanos, a very considerable por- 
tion has a temperate climate. It is in these temperate zones that 
mining 1s now carried on. Fora full account of the physical geog- 
raphy and climatology of Colombia the reader may consult ‘“*The 
Earth and its Inhabitants—S. America,” vol. 1, by Elisée Reclus. : 
According to Dana the highest peaks of the Eastern Cordillera 
are Upper Cretaceous. Prestwich, following David Forbes and M. 
Pissis, states that in the Andean regions the Quaternary of the coast 
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