282 The Andes and the Amazon. 



pent-up waters of the valley. The table-topped hills of 

 Almeyrim are almost the sole relics.* Finally, over the 

 undulating surface of the denuded sandstone an ochra- 

 ceous, unstratified sandy clay was deposited. 



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 deposit brought down from the Andes and 

 worked over by the melting of the ice which transported 

 it.t The Professor farther 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 ; ter- 

 tiary deposits have never been observed in any part of the 

 Amazonian basin." This was true up to 1867. Neither 

 Bates, Wallace, nor Agassiz found any marine fossil on the 

 banks of the great river. But there is danger in building 

 a theory on negative evidence. These explorers ascended 

 no farther than Tabatinga. Two hundred miles west of 

 that fort is the little Peruvian village of Pebas, at the con- 

 fluence of the Ambiyacu. We came down the Napo and 

 Maranon, and stopped at this place. Here we discovered a 

 fossiliferous bed intercalated between the variegated clays 

 so peculiar to the Amazon. It was crowded with marine 

 tertiary shells ! This was Pebas vs. Cambridge. It was 

 unmistakable proof that the formation was not drift, but 

 tertiary ; not of fresh, but salt water origin. The species, 



* " On the South American coast, where tertiary and supra-tertiary beds 

 have been extensively elevated, I repeatedly noticed that the uppermost beds 

 were formed of coarser materials than the lower ; this appears to indicate 

 that, as the sea becomes shallower, the force of the waves or currents in- 

 creased." — Darwin's Observations, pt. ii., 131. " Nowhere in thePampas is 

 there any appearance of much superficial denudation." — Pt.iii., 100. 



t A Journey in Brazil, p. 250, 411, 424. Again, in his Lecture before 

 the Lowell Institute, 1866 : " These deposits could not have been made by 

 the sea, nor in a large lake, as they contain no marine nor fresh-water fossils." 



