GEOLOGY OP PERU — ADAMS, 42*7 



of rocks, probably Carboniferous, form the great basin of Lake Titi- 

 caca, and a small spot in the heights of Huanta. 



In his volume on the Department of Ancachs (1873) he elaborates 

 his ideas somewhat more fully. He says that the first land relief 

 produced within the limits of Peru was not the Cordillera which 

 forms the continental divide, but the grand mountain chain which 

 in Bolivia forms the Cordillera real and extends northward into 

 Peru. 



This grand chain is formed for the most part of talcose and clay 

 slates and owes its relief to the eruption of granitic rocks, which, 

 however, did not always find their way to the surface, being rare 

 in the southern part of the chain, but in many places the eruption 

 introduced quartz veins into the slates. Contemporaneous with this 

 relief jDerhaps occurred the eruption of the granites and syenites of 

 the coast, which in many places contain thin veins of auriferous 

 quartz. 



After the Jurassic began the eruption of the porphyries, and when 

 the Cretaceous had begun the grand eruption of the diorites took 

 place. Following the deposition of the Cretaceous the axis of the 

 Cordillera was brought into relief. 



A sketch of the geology of South America was read by Steinmann 

 before the Geological Society of America in 1891. This sketch is 

 explanatory of a map which was prepared by him for a second edi- 

 tion of Berghausen's Physical Atlas. Unfortunately the map is very 

 small, and, moreover, data were not available for an accurate map. 

 From the sketch the following points may be gathered which are 

 of interest here. 



In Devonian times, as is indicated by the sediments, there was an 

 extensive sea embracing the larger part of South America, especially 

 Brazil and Bolivia (and extending also into Peru). 



The Carboniferous deposits were more restricted, but are known 

 from Peru, Bolivia, and Brazil. 



During the Permian, Triassic, and Jurassic the greater part of 

 the South American continent was above sea level; however, the 

 Triassic and Jurassic marine deposits have been found on the western 

 part of the continent, rich collections of Jurassic fossils having been 

 obtained from the Cordilleras of the Argentine, Chile, and Peru. 



In contrast to the small extension of marine Triassic and Jurassic 

 the Cretaceous covers a large area, marine Cretaceous being found 

 in all parts of the Cordillera of the Andes from Venezuela to 

 Patagonia. 



The Cordillera of South America is famous for its eruptive forma- 

 tions of the latest time, but it merits no smaller attention for its 

 submarine eruptions during Mesozoic time and the injection of the 

 Mesozoic strata by dioritic rocks. 



