GEOLOGY OF PERU—ADAMS. 423 
7. Zone of slates (Silurian) and granites. 
Comparing these zones with those enumerated by Steinmann, later 
to be mentioned, it will be seen that there are no granitic rocks in 
the coast and that the coast range which extends from Arica south- 
ward into Chile is not comparable with the coast range at Mollendo. 
Tn fact, there is a gap between the two just north of Arica. In other 
respects the zones are quite comparable excepting for the difference 
due to the structure of the Titicaca basin. The rocks which Forbes 
called “ Permian” or “ Triassic” are now called “ Cretaceous” by 
Steinmann, and above are included with the Mesozoic. 
SECTION THROUGH THE DEPARTMENT OF ANCACHS, BY RAIMONDI (18738). 
Tt should be remembered in considering this region that the Cor- 
dillera Occidental divides into two branches, the western known as 
the “ Cordillera Negra” and the eastern or principal one, the “ Cor- 
dillera Blanca.” Raimondi made no section, but from his writings 
one may recognize the following zones: 
1. Granites and syenites of the coast. 
2. Mesozoic sediments with porphyries and diorites. The sedi- 
mentaries are rare in the coast but are found more abundantly inland. 
3. The diorites are seen in the Cordillera Negra and the Cordillera 
Blanca up to the limit of snow, but not in the crest of the range or 
axis. The eruption of the diorites posterior to the Jurassic removed 
and lifted some formations of the Cretaceous and introduced metallic 
veins. 
4, 'Trachytes anterior to the present, there now being no volcanoes. 
These rocks are present in the Cordillera Blanca and to some extent 
in the Cordillera Negra but not forming peaks in the latter. Rai- 
mondi thinks the eruption of the trachytes occurred at a time when 
the two Cordilleras formed one mass and that they have since been 
separated by erosion. 
- 5. In the valley of the Maranon are found older sediments, talcose 
slates with quartz veins which are referred to the Silurian. A small 
area of similar rocks was also noted at Pallasca on the western slope 
of the Cordillera Nevada. 
SECTION OF ECUADOR, BY WOLF (1892). 
Reviewing the geology of Ecuador as outlined by Wolf and co- 
ordinating the data in such a way as to compare it with the sections 
already given of Peru we find the following more or less distinct 
zones: 
1. The Tertiary and Quaternary formations of the coast of marine 
origin. 
88292—sm 1908——28 
