426 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1908. 



that he breaks the contmuity of the Cretaceous in the Andes between 

 northern Peru and Ecuador, so that the Tertiary of the Pacific coast 

 connects with the Tertiary of the Amazon basin in the latitude of 

 the Gulf of Guayaquil. D'Orbigny also published four small maps 

 showing the development of the South American continent. He took 

 as a nucleus a small area of gneissic and primordial rocks along the 

 Brazilian coast. From this area the land mass developed to the 

 northwest. After the Carboniferous he shows a land mass in Guiana 

 in addition to the larger one in Brazil. After the Triassic he shows 

 an isolated land mass in the eastern Cordilleras of Peru and Bolivia, 

 and following the Cretaceous he unites the Brazilian and Andean 

 land masses by a fringing border of Cretaceous, and shows an isolated 

 mass of Cretaceous in Ecuador and Colombia and Venezuela. The 

 remaining parts of the continent were formed by the addition of 

 Tertiary and diluvial. [The maps by d'Orbigny are of only his- 

 torical interest as showing the development of geological science at 

 that time.] 



Agassiz appears to have followed in a measure the ideas advanced 

 by d'Orbigny. He says in substance (1868) that the valley of the 

 Amazon was first sketched out by the elevation of two tracts of land, 

 namely, the plateau of Guiana on the north and the central plateau 

 of Brazil on the south. It is probable that, at the time these two 

 tablelands were lifted above the sea level, the Andes did not exist and 

 the ocean flowed between them through an open strait. At a later 

 period the upheaval of the Andes took place, closing the western side 

 of this strait and thus transformed it into a gulf open toward the 

 east. It seems certain that at the close of the secondary age the whole 

 Amazon basin was lined with a Cretaceous deposit, the margins of 

 which crop out at various localities on its borders. They have been 

 observed along its southern limits on its western outskirt along the 

 Andes, in Venezuela along the shore line of mountains, and also in 

 certain localities near its eastern edge. 



Orton evidently followed the ideas advanced by Agassiz, but his 

 poetical and cataclastical account of the geological development of 

 South America is of no value to science. He says, for example: 

 " Three times the Andes sank hundreds of feet beneath the ocean 

 level and again were slowly brought up to their present height." 



The first attempt which Raimondi made to outline the geology 

 of Peru was in his letter to Gabb (1867). He stated that the eastern 

 Cordillera is of greater age geologically, appearing to be composed 

 of micaceous and talcose slates which have been metamorphosed by 

 the elevation of the granites, that have also introduced numerous 

 veins of quartz which in some places are quite rich in gold. The 

 western Cordillera, he says, is made up in nearly the whole of its 

 length of rock of much more recent age (Mesozoic). Another group 



