562 The Andes and the Amazons. 



have retained their colors and epidermis, and the bivalves 

 generally .occur with the valves united and closed. They 

 exist also in such vast numbers, they must have lived and 

 died on the spot. The bivalves are most abundant at 

 Pichana, and the univalves at Iquitos — localities at least 

 150 miles apart: the former may be the lower stratum, 

 and the otlier the upper. The Hernisintis is particularly 

 abundant at Iquitos, and very rare in the Pebas district. 

 Mr. Gabb led me astray in saying, on page 282, that these 

 shells are marine. Most of them are fresh-water, many 

 are estuary (but might have lived in fresh or brackish 

 water), and a few are terrestrial. Mr. Conrad, who exam- 

 ined my large collections, and is better prepared to speak 

 than any other paleontologist, considers the beds Eocene.^ 

 I am not prepared to give the vertical or horizontal dis- 

 tribution of these fossils. So far as visible at low water, 

 they appear to I'ange over twenty feet of depth, coming 

 nearer to the surface at Pebas than at Iquitos ; but the main 

 layer lies nearly parallel with the level of the river, which 

 falls about forty feet between the two places. They oc- 

 cur on both sides of the lignite, which is traceable from 

 Tabatinga to the Huallaga. The shell-bed must extend 

 far west of Iquitos ; and in my last expedition, I procured 

 a mass of yellow clay containing the " Pebas shells" from 

 a point several hundred miles up the Ucayali ; the precise 

 locality I can not give, as I did not visit it. Evidently this 

 Tertiary basin is not so contracted as the glacialists have 

 tried to make it. Dr. Gait brought from the Pachitea 

 (near the junction of the Pichis and Palcazu) a beautiful 

 Ostrea, which Conrad calls 0. callacta, and says it is a Ter- 

 tiary form, and was filled with a light-colored clay strik- 



* Per contra, Professor Hartt, who has never seen the Maranon, decides 

 that " it was in the latter part of the stage of growth of the basin that the 

 days of the Upper Amazon were deposited, and the Pebas shells lived. 

 This appears to have been near the close of the Tertiary." 



