170 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1917. 



favorable results. The glaciation probably would have destroyed 

 any placers which may have existed in this region, and this guide 

 for the prospector is, therefore, generally lacking. 



V. COMPARISON OF THE TWO CONTINENTS. 



It has been shown that the pre-Cambrian and early Paleozoic gold 

 deposits predominate in the eastern part of North and South Amer- 

 ica; that they are scattered irregularly over a wide territory and do 

 not form well-defined belts except locally; and that the heavy pro- 

 duction is very much localized. There is reason to believe that such 

 deposits occur here and there in the pre-Cambrian rocks of the 

 cordilleran regions, though they are not easily differentiated from 

 the later cordilleran period of mineralization. We note the marked 

 localization of rich deposits in the Black Hills and in the Porcupine, 

 which may be compared to the strongly auriferous districts of the 

 Guianas and Minas Geraes. We observe, also, that as far as this 

 earliest mineralization is concerned, both continents are about equally 

 rich. No silver deposits of this period, such as are concentrated to 

 such a remarkable degree at Cobalt, Ontario, are Imown from South 

 America. 



In the cordilleran region of South America the principal and 

 almost the only period of mineralization seems to be that of the early 

 Tertiary, while in North America an important series of deposits 

 dates from the early Cretaceous. The batholithic and smaller in- 

 trusions in South America all appear to date from early Tertiary, 

 and the evidence of close connection between intrusion and minerali- 

 zation is cumulatively strong and convincing. The same general prin- 

 ciples of association of the two agencies apply in the two continents. 



So far, no definite evidence has been adduced that the great lava 

 flows of the Jurassic and Cretaceous contain mineral deposits of that 

 general age. In North America many intrusions — in fact the gi^eatest 

 batholiths — date from the earliest Cretaceous. No such occurrences 

 are found in South America. 



From northern Mexico to Chile the Cretaceous is by far the most 

 prominent of the sedimentary formations, while the Carboniferous 

 limestone, so important for the mineralization of the Cordilleras in 

 the United States, is entirely lacking. 



Another interesting feature is the great scarcity in South America 

 of Tertiary deposits of gold and silver occurring in late Tertiary 

 lavas and formed close to the surface. Popularly the majority of 

 deposits in South America are ascribed to this group, and- even the 

 latest textbooks fall into this error. There are some of these inter- 

 esting and rich deposits in the southern Provinces of Colombia, but 

 none have been recorded in Peru and Bolivia, In Chile they re- 



