
THE MINING DISTRICTS AND ORES OF TOLIMA. 
The Magdalena River, from its source two degrees north of the 
equator, to about six degrees north where it touches the Depart- 
ments of Antioquia and Cundiamarca, flows in a deep, longitudinal 
valley, between the Eastern and Central Cordilleras of the Andes. 
This valley, between the crests of the two Cordilleras, and between 
the above indicated north and south limits, forms the Department 
of Tolima, the second in importance of the mining states of Colombia. 
According to John C. Randolph,* who has studied the geology 
of this region, the Magdalena flows in a synclinal valley. Under the 
alluvion of the valley lies a red Triassic sandstone which overlies 
Archean schists. The schists outcrop in a broad zone at an elevation 
of between 4,000 and 5,000 feet. On the west side of the valley 
patches of Jurassic limestone overlie the sandstone in places, and on 
the east these Jurassic limestones are of great thickness. The schists 
are penetrated and overlain everywhere with andesites and other 
eruptive rocks. Inthe collection under consideration these eruptives 
are represented by andesites, trachytes and rhyolites. 
Mr. Randolph found that the veins of Tolima are quartz inter- 
calated in the schists. The veins tend to wedge out and reappear. 
No true vein cutting across the schists has been found. The collec- 
tions in the Museum show in addition to this that the ores, although 
often occurring in the mica schists, are found only in the vicinity of 
eruptive rocks. 
In the early days of mining in the Department of Tolima the 
cities of San Sebastian de la Plata in the south, and Mariquita in the 
north, were the centers about which the mining districts were 
grouped. From a variety of causes, including attacks from hostile 
Indians and the prohibition of enforced Indian labor, the mines were 
abandoned for many years, and even the locations of many of them 
were forgotten. From the localities given by Sefior Gamba in his 
catalogue, it appears that the revival of mining in recent times has 
taken place almost wholly in the northern districts, in the vicinity 
of the active volcano of Tolima. These districts were of old, trib- 

*Tr. A. I. M. E. Vol. XVIII, 1889, p. 208. 
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