GOLD AND SILVER DEPOSITS LINDGREN. 149 



value of $99,476,400, South America's mines yielded less than one- 

 tenth of this huge sum. Figure 1 shows the approximate distribution 

 of the gold and silver deposits of the two continents. 



There are no better prospectors in the world than those of some 

 South American countries, and we may rest assured that a great 

 percentage of possible discoveries has already been made. Yet no 

 one who has studied South American mining districts can fail to 

 see the possibility of a more extended production than at present, 

 even while realizing the difficulties of climate, altitude, transporta- 

 tion, and lack of adequate available capital. 



The purpose of this paper is to call attention to the geological 

 features that govern the distribution and richness of the precious 

 metal deposits of South America, to compare them with those of 

 North America, and to classify them according to geological 

 affiliation. 



II. GEOLOGICAL FEATURES. 



A slight acquaintance with the geographic features of the two 

 parts of the American Continent suffices for the realization of their 

 essential similarity. The two land masses, elongated from north to 

 south, have a wide eastern part occupied by fertile plains, hilly 

 country or low mountain ranges, and a narrower western part, with 

 the rough topography of an almost continuous high mountain chain 

 closely following the Pacific coast, narrow in South America, broad- 

 ening in North America. This is one of the great earth features, 

 and is known as the American Cordillera. In South America it is 

 also known as the Andes. Considered on a large scale, its build is 

 simple, though in detail it is diversified by two or more parallel 

 ranges, by intermontane high plateaus or valleys, and by volcanoes, 

 many of which are active. 



To the geologist this difference of east and west is sharply accen- 

 tuated, for he knows that the Atlantic side represents the area of 

 (juiet where strong mountain-building forces have rested for millions 

 of years — since the close of the Paleozoic era — while the leveling 

 agencies of erosion and sedimentation have been at work. He knows 

 that the western margin marks the long strip of weakened eartli 

 crust along which tangential stresses have played since early Meso- 

 zoic times. These stresses cuhninated in the early Tertiary times, 

 causing folding and violent thrust faulting, as if an irresistible force 

 had forced a wrinkle in the earth's crust eastward. These cordil- 

 leran disturbances reach their maximum along the inner eastern edge 

 of the chain. To some degree they still continue, accompanied by 

 uplifts and depressions. Lava flows have been poured out in great 

 volume from volcanoes along the Cordilleras, especial!}^ on the west- 

 ern side, and this has continued at least from the early Mesozoic to 



65133°— sji 1917 11 



