HISTORICAL REVIEW OF THE GEOLOGICAL EXPLO- ° 
RATION OF THE WESTERN PART OF THE PROVINCE 
LA RIOJA. 
In the mining history of the Argentine Republic the province of 
La Rioja plays a very important part. Already since times of the 
spanish jesuits work has been done in these distant and desertous 
. mountains for the search and exploitation of many rich minerals of 
gold, copper and silver. Especially in the famous Nevado de Fama- 
tina the mining work has been very productive. A rational exploi- 
tation of the ores there began, however, about fifty years ago, and 
since this time the mining industry here has been in a steady pro- 
gress. The newly built railway from Serrezuela (Prov. de Cordoba) 
to Chilecito (situated on the eastern side of the Nevado de Fama- 
tina) and the electric wire rail from Chilecito up to the mines of 
La Mejicana, in an alture of about 5000 m. (ab. the sea) on the E 
slopes of the Nevado, give an evidence of the intensity of exploi- 
tation in the last times. At present (1917) the whole business is, 
in consequence of various circumstances, stopped.! 
In comparison with the extensive prospecting work of all the re 
tal occurrences in these regions, the progress of the geological ex- 
ploration has been quite insignificant, especially when regarding the 
old crystalline rocks, appearing as the main components of the 
mountain blocks of the Sierra de Velazco, the Sierra de Famatina 
and the Sierra de Umango. 
1 Regarding the mining history of the Nevado de Famatina, see: A. Stelzner 
(1876--1885), and E. Hermitte: La mineria argentina. Buenos Aires 1915. 
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