THE AMAZON VALLEY. 283 



It is above the Madeira that we first meet with the curious 

 phenomenon of great rivers of black water. The Rio Negro 

 is the largest and most celebrated of these. It rises in about 

 2 30' N. lat, and its waters are there much blacker than in 

 the lower part of its course. All its upper tributaries, the 

 smaller ones especially, are very dark, and, where they run 1 

 over white sand, give it the appearance of gold, from the rich 

 colour of the water, which, when deep, appears inky black. 

 The small streams which rise in the same district, and flow 

 into the Orinooko, are of the same dark colour. The Cassi- 

 quiare first pours in some white or olive-coloured water. 

 Lower down, the Cababuris, Maraviha, and some smaller 

 white-water streams help to dilute it, and then the Rio Branco 

 adds its flood of milky water. Notwithstanding all this, the 

 Rio Negro at its mouth still appears as black as ink ; only in 

 shallow water it is seen to be paler than it is up above, and the 

 sands are not dyed of that pure golden tint so remarkable 

 there. 



On the south of the Amazon there are also some black- 

 water streams the Coary, the Teffe, the Juru, and some 

 others. The inhabitants have taken advantage of these, to 

 escape from the plague of the mosquitoes, and the towns of 

 Coary and Ega are places of refuge for the traveller on the 

 Upper Amazon, those annoying insects being scarcely ever 

 found on the black waters. The causes of the peculiar colour 

 of these rivers are not, I think, very obscure ; it appears to me 

 to be produced by the solution of decaying leaves, roots, and 

 other vegetable matter. In the virgin forests, in which most 

 of these streams have their source, the little brooks and rivulets 

 are half choked up with dead leaves and rotten branches, 

 giving various brown tinges to the water. When these rivulets 

 meet together and accumulate into a river, they of course have 

 a deep brown hue, very similar to that of our bog or peat 

 water, if there are no other circumstances to modify it. But 

 if the streams flow through a district of soft alluvial clay, the 

 colour will of course be modified, and the brown completely 

 overpowered ; and I think this will account for the anomalies 

 observed, of streams in the same districts being of different 

 colours. Those whose sources are pretty well known are seen 

 to agree with this view. The Rio Negro, the Atabapo, the 

 Isanna, and several other small'er rivers, have their sources 



