GEOLOGY OF PERU—-ADAMS. AD4 
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 perhaps 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. 
