GEOLOGY. 245 



exactly in their character to materials accumulated in glacier bot- 

 toms; secondly, .in the resemblance of the upper or third Ama- 

 zonian formation to the Rio drift, of the glacial origin of which 

 there cannot, in my opinion, be any doubt; thirdly, in the fact 

 that these fresh-water basins must' have been closed against the 



!^ 



sea 'by some powerful barrier, the removal of which would natu- 

 rally give an inlet to the waters, and cause the extraordinary 

 denudations, the evidences of which meet us everywhere through- 

 out the valley." 



Professor James Orton differs from Agassiz altogether in his 

 views of this formation. He says : 



" It is a question to what period this great accumulation is to 

 be assigned. Humboldt called it Old' Red Sandstone; Martins 

 pronounced it New Red; Agassiz says Drift, the glacial de- 

 posit brought down from the Andes and worked over by the 

 melting of the ice which transported it. The professor further 

 declares that * these deposits are fresh-water deposits ; they show 

 no sign of a marine origin ; no sea-shells nor remains of any 

 marine animal have as yet been found throughout their whole 

 extent ; tertiary deposits have never been observed in any part 

 of the Amazonian basin.' It is true that neither Bates, Wallace, 

 nor Agassiz found any marine fossils on the banks of the great 

 river, but these explorers ascended no farther than Tabatinga. 

 Two hundred miles west of this fort is the little village of Pebas, 

 at the confluence of the Ambiyacu. In the high bank on which 

 the village stands, I discovered a fossiliferous bed interstratified 

 with the variegated clays so peculiar to the Amazon. It was 

 crowded with marine tertiary shells. The species, as determined 

 by W. M. Gabb, Esq., of Philadelphia, are Neritina pupa, Turbon- 

 illa minuscula, Mesalia Ortoni, Tellina Amazonensis, Pachydon (gen. 

 not'.) obliqua, arid PacJtydon tenua. It is a singular fact that the 

 Neritina is now living in the West India waters, and the species 

 found at Pebas retains its peculiar markings ; so that we have 

 some ground for the supposition that not many years ago there 

 was a connection between the Caribbean Sea and the upper 

 Amazon ; in other words, that Guiana has only very lately ceased 

 to be an island. Interstratified with the clay deposit are seams 

 of a highly bituminous lignite ; we traced it from near the rnouth 

 of the Curaray on the Rio Napo to Loreto on the Maraiion, a 

 distance of about 400 miles. It occurs also at Iquitos. This is 

 further testimony against the glacial theoiy of the formation of 

 the Amazonian valley. The paucity of shells in such a vast de- 

 posit is not astonishing. It is remarkable in the similar accumu- 

 lation of reddish argillaceous earth, called Pampean mud, which 

 overspreads the Rio Plata region. Some of the Pampa shells, 

 like those at Pebas, are proper to brackish water, and occur only 

 on the highest banks. The Pampean formation is believed by Mr. 

 Darwin to be an estuary or delta deposit." Orton. The Andes 

 and the Amazon. Nero York, 1870, page 878 and folio icing ; and 

 Proceedings Amer. Assoc. Adv. Sci., xviii. (1869), pages 195-199. 



At the meeting of the American Association at Troy, 1870, 

 Professor Orton exhibited specimens of shells which have since 



21* 



