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. Rozier, 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 



* Voyage to the river Congo, p. 488. 



