20 



so extraordinary? We must observe in the first 

 place, that this phenomenon does not belong to 

 the cataracts of the Oroonoko alone, but is found 

 in both hemispheres. At my return from Mexi- 

 co in 1807, when I showed the granites of Atu- 

 res and Maypures to Mr. Roziere, who had tra- 

 velled over the valley of Egypt, the coasts of the 

 Red Sea, and Mount Sinai, this learned geolo 

 gist let me see, that the primitive rocks of the 

 little cataracts of Syene display, like the rocks 

 of the Oroonoko, a glossy surface, of a blackish 

 gray, or almost leaden colour, and of which 

 some of the fragments seem coated with tar. 

 Recently, in the unfortunate expedition of Cap- 

 tain Tuckey, the English naturalists were struck 

 with the same appearance in the yellalas (ra- 

 pids and shoals) that obstructed the river Congo 

 or Zaire. Dr. Kcenig has placed in the British 

 Museum, by the side of the syenites of the Con- 

 go, the granites of Atures taken from a series of 

 rocks, which were presented by Mr. Bonpland 

 and myself to the illustrious president of the 

 Royal Society of London. " These fragments," 

 says Mr. Kcenig*, " alike resemble meteoric 

 stones ; in both rocks, those of the Oroonoko 

 and of Africa, the black crust is composed, ac- 

 cording to the analysis of Mr. Children, of the 

 oxyd of iron and manganese." Some experiments 



*- V >yage to the river Congo y p. 488. 



