GEOLOGY OF PERU—ADAMS. 395 
of clay slates, shales, and quartzites, but he found no limestones. The 
fossils which he collected were examined by Salter and showed that 
probably the whole Silurian is represented. Forbes called attention 
to the fact that the formation contains quartz veins, and that these 
have given rise to auriferous gravels. He contradicted the state- 
ment of d’Orbigny that the peak Illimani in Bolivia is a granite 
peak as shown in the section, and says that Illimani and Ilampu 
(Sorata) are composed of slates. 
Raimondi (1867) described the Cordillera Occidental as contain- 
ing slates cut by quartz veins carrying gold, and later (1873) in out- 
lining the geology of the Department of Ancachs he classes the 
slates as Silurian. 
In southern Peru Balta (1897) has classed the slates in the Prov- 
ince of Carabaya and Sandia as Silurian because of the presence of 
graptolites, and this classification was followed by Pflucker* who, 
however, contributed little to our knowledge of the Silurian. 
Ochoa, in his bulletin® on the Province of Huanuco, in the central 
part of the Peruvian Andes, makes a brief reference to the finding of 
graptolites near Huacar, from which fact he concluded that the 
Silurian is present there. 
Steinmann (1904) identified by means of graptolites the lower 
Silurian in the region of Tarma, also in the central region of the 
Peruvian Andes, and he states that the granite associated with the 
Silurian in the Cordillera Oriental made its appearance in lower 
Silurian time. 
Farther to the north Raimondi (1873), in describing the geology 
of the Department of Ancachs, states that in the Province of Huari, 
near Uco, in the valley of the Maranon, there are older sediments with 
a great formation of talcose slates with quartz veins, which he refers 
to the Silurian, although he did not mention any fossils. He also 
states that there is a similar area on the western slope of the Cordil- 
lera Nevada (Occidental) at Pallasca. Farther to the north and in 
the foothills of the Cordillera Occidental, in passing over the divide 
from Motupe to Olmos and in the vicinity of Olmos, the writer saw 
extensive exposures of slates cut by numerous quartz veins and 
stringers which have been prospected for gold. Mention is here made 
of the area because of its resemblance to the Silurian, but it should 
not be definitely classed until fossils have been found. 
A paper which has an important bearing on the paleontology of 
the Silurian was published by A. Ulrich (1892) describing an ex- 
“Informe sobre los yacimentos auriferous de Sandia, Bol. del Cuerpo de 
Ingenieros de Minas del Peru No. 26, 1905, Luis Pflucker. 
> Recursos minerales de la provincia de Huanuco, Bol. del Cuerpo de In- 
genieros de Minas del Peru No. 9, 1904, Nicanor G. Ochoa. 
