426 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1908. 
that he breaks the continuity of the Cretaceous in the Andes between 
northern Peru and Kcuador, 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 toek 
as a nucleus a small area of gneissic and primordial rocks along the 
Brazilian coast. Krom 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 
