GEOLOGY OF PERU ADAMS. 395 



of clay slates, shales, and quartzites, but lie 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 Illampu 

 (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 gi-anite 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 DejDartment 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 Ohnos 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. 



