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 Eed Sandstone ;" 

 Martins pronounced it " l\ew Eed ;" Agassiz says " Drift" 

 — the glacial deposit brought down fi'om the Andes and 

 worked over by the melting of the ice which transported 

 it.f 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. l^either 

 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 Xapo 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 m. 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-tertiaiy 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 the Pampas is 

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



t A Journey in Brazil, p. 250, 411, 42-t. 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." 



