GOLD AND SILVER DEPOSITS LINDGREN. 161 



the pre-Cordilleras. In the extreme north, in Salta and Jujuy 

 Provinces, really the continuation of the Bolivian Altiplanicie, the 

 Paleozoic rests, according to Keidel, 1 with marked discordance on 

 phyllites and quartzites of probably pre-Cambrian age. 



In the eastern main Cordillera the marine Mesozoic (Jurassic and 

 Cretaceous) rests unconformably on the basement of Paleozoic slates 

 and includes great masses of flows of " quartz porphyries " and 

 " melaphyres," i. e., rhyolites and basalts. 



In the pre-Cordillera of San Juan and Mendoza 2 there are heavy 

 continental deposits of upper Carboniferous to Upper Triassic age, 

 resting on a Paleozoic folded basement. According to I. Bowman 

 and other geologists these pre-Cordilleras continue northward into 

 Bolivia and here also consist, in large part, of continental sandstone 

 deposits. Small areas of porphyries and granite are intruded in 

 these rocks. The series is gently folded toward the east. 



On the eastern slopes of the Andes, sedimentary rocks generally 

 predominate. Two periods of folding are recognized — an older 

 Paleozoic and a younger Tertiary movement, the latter being desig- 

 nated as the properly Anclene disturbances. Along the eastern bor- 

 der the latter is marked by overthrusts and overturned folds. 



IV. DISTRIBUTION OF SOUTH AMERICAN DEPOSITS OF GOLD 



AND SILVER. 



In the following paragraphs a brief summary is given of the dis- 

 tribution of the precious metal deposits in each of the cordilleran 

 States of South America. 



COLOMBIA. 



In Colombia we find the principal gold belt of the Andes, which 

 under adverse circumstances yields annually a notable production of 

 $3,000,000 to $4,000,000. This production is probably capable of con- 

 siderable expansion. 3 The total yield of that country, as calculated 

 by Vincente Eestrepo, amounts to about $700,000,000; therefore 

 Colombia takes its place among the great gold-producing regions 

 of the world. 



The deposits are mainly in the western and central ranges, which 

 do not continue northward into Panama, but bend eastward toward 



1 Ueber den Bau der Argentinischen Anden ( Sitzungsberichte der Kaiserlichen- 

 KOniglichen Akademie der Wissenschaften (Wien, 1907). Pp. 649-674, Bd. CXVI. AGT. I.). 

 Die neueren Ergebnisse der Staatlichen geologischen Untersuchungen in Argentinien 

 (Compte Rendu, 11th session Congres G6ologique International, Stockholm, pp. 1127 to 

 1141 (1910).)- 



2 R. Stappenbeck : La Pre-Cordillera de San Juan y Mendoza (Anales, Ministerio de 

 Agricultura, Seccion geologiea, Tomo iv, No. 3 (Buenos Aires). ). 



3 The latest statistics for 1914 show a very marked increase in the production of 

 Colombia, the figure being $4,678,600. 



