424 A JOURNEY IN BRAZIL. 



allow the accumulation of these materials, and its sub- 

 sequent elevation. I reject this explanation for the simple 

 reason that the deposits show no sign whatever of a 

 marine origin. No sea-shells, nor remains of any marine 

 animal, have as yet been found throughout their whole 

 extent, over a region several thousand miles in length 

 and from five to seven hundred miles in width. It is 

 contrary to all our knowledge of geological deposits to 

 suppose that an ocean basin of this size, which must have 

 been submerged during an immensely long period in order 

 to accumulate formations of such a thickness, should not 

 contain numerous remains of the animals formerly inhab- 

 iting it.* The only fossil remains of any kind truly belong- 

 ing to it, which I have found in the formation, are leaves 

 taken from the lower clays on the banks of the Solirnoens 

 at Tonantins ; and these show a vegetation similar in 

 general character to that which prevails there to-day. 

 Evidently, then, this basin was a fresh-water basin ; these 

 deposits are fresh- water deposits. But as the valley of 



* I am aware that Bates mentions having heard that at Obydos cal- 

 careous layers, thickly studded with marine shells, had been found interstrat- 

 ified with the clay, but he did not himself examine the strata. The Obydos 

 shells are not marine, but are fresh-water Unios, greatly resembling Aviculas, 

 Solens, and Areas. Such would-be marine fossils have been brought to me 

 from the shore opposite to Obydos, near Santarem, and I have readily rec- 

 ognized them for what they truly are, fresh-water shells of the family of 

 Naiades. I have myself collected specimens of these shells in the clay-beds 

 along the banks of the Solimoens, near TefFe, and might have mistaken 

 them for fossils of that formation had I not known how Naiades burrow in 

 the mud. Their resemblance to the marine genera mentioned above is very 

 remarkable, and the mistake as to their true zoological character is as nat- 

 ural as that by which earlier ichthyologists, and even travellers of very recent 

 date, have confounded some fresh-water fishes from the Upper Amazons, of 

 the genus Pterophyllum (Heckel), with the marine genus Flatax. 



