23 



tion ; and this idea is no way at variance with 

 the phenomena, that we daily observe in our 

 laboratories. The waters of great rivers con- 

 tain carbonic acid ; and, were they even entirely 

 pure,, they would still be capable, in very great 

 volumes, of dissolving some portions of oxyd, or 

 those metallic hydrats, which are regarded as 

 the least soluble. The mud of the Nile, which 

 is the sediment of the matters that the river 

 holds suspended, is destitute of manganese; 

 but contains, according to the analysis of Mr. 

 Regnault, six parts in a hundred of oxyd of 

 iron ; and it's colour, at first black, changes to 

 yellowish brown by desiccation and the con- 

 tact of air*. The mud consequently is not the 

 cause of the black crusts on the rocks of Syene. 

 Mr. Berzelius had the goodness, at my request, 



* The mud of the Nile contains. 



Water 11 



Carbon 9 



Oxyd of iron 6 



Silex 4 



Carbonat of Magnesia 4 



Carbonat of lime....... .. 18 



Alumin . 48 



100 



(Observations sur la Vallee d'Egypte, par M. Girard, p. 64.) 

 I filtered at Atures the water of the Oroonoko ; and it ap- 

 peared to me, to contain nothing but quartzose sand, and 

 many spangles of mica. 



