Structure of the Amazons Valley. i$G5 



from a higher locality further south*. The Andean region 

 was covered by the Jurassic sea, and was afterward elevated 

 (in Northern Peru) 11,000 feet. The moment the Andes began 

 to rise, the topography of the Amazons valley was fore- 

 shadowed. The superficial Cretaceous strata up the Parana- 

 pura, at the Pongo de Manseriche, and from Tomependa up 

 the remarkable longitudinal valley of the Upper Marafion to 

 Balsas, into the department of Ancachs, would indicate that 

 so much at least of the great river began to exist in the 

 early Tertiary. Without doubt, during the Cretaceous period 

 the Atlantic and Pacific were continuous oceans, flowing over 

 not only the Panama isthmus, but also over all Equatorial 

 America, save a few islands and reefs. We are not surprised 

 therefore to find the same Cretaceous (and even Miocene) 

 species on both sides of the Andesf, 



The vast basin (whether Carboniferous or Cretaceous I will 

 not say) formed by the rise of the Andes and the metamorphic 

 regions on the north and south received an immense sheet of 

 coloured clays, sands, and sandstones. This deposit, unique in 

 its extent and origin, is known as the Amazonian Tertiary 

 formation. It was the sediment of a brackish Mediterranean, 

 or of a quiet lake to which brackish water had occasional 

 access. The argillaceous and loamy beds are universal ; the 

 sandstone has been reduced by subsequent denudation, and is 

 now nearly confined to the Lower AmazonsJ. Excepting this 



under the name of T. miUepunctata, among some specimens brought from 

 Santa Cruz by Mr. Cummings (Quart. Journ. Geol. Soc. vol. xvii. p. 50) ; 

 and Toula describes an apparently identical form from Cochabamba as T. 

 Hoehstetteri (Proc. Vienna Acad. lix.). Ryhnchonella or Camaro- 

 phoria, sp. : a small specimen ; ovate, about as long as wide ; ventral 

 valve depressed, convex, with a broad shallow sinus extending but little 

 beyond the middle, and marked by two rounded ribs ; dorsal valve gibbous ; 

 surface smooth. Should this prove to be new, I would suggest the name 

 of R. (or 0.) Ortonii. Of these species, S. camerata, S. perplexa, and E. 

 Mormonii occur on the Tapajos in beds equivalent to the North-American 

 Coal-measures, of which the same species, with T. bovidens, are charac- 

 teristic. I have endeavoured to show (Bull. Cornell Univ. vol. i. part 2, 

 p. (5) that the fossils found in various Bolivian localities belong to the 

 same division of the Carboniferous age. The existence of a Carboniferous 

 basin in Peru quite widely removed from the Titicaca basin on the south, 

 and from the Tapajos basin on the east, is an exceedingly interesting- 

 point in South- American geology. 



* Dr. Gait brought an Ammonite from the mouth of the Pichis on the 

 Pachitea (Upper Ucayali ), which appears to be Cretaceous. It was pro- 

 bably washed down from the south. 



t Mr. Bland informs me, after an examination of my land-shells, that 

 the general aspect of the living Bulimi from the Peruvian Andes is 

 remarkably like the Lower Californian. 



% Vesicular ferruginous sandstone occurs far up the Madeira and 

 Negro. I am not aware of its existence in any part of the Maranon 

 region. 



