TRIBUTARIES OF THE AMAZONS. 



39 



stream to a height of twelve or fifteen feet, and then collapses 

 with a roar so dreadful that it is heard at the distance of more 

 than six miles. Then the advancing flood-wave glides almost 

 imperceptibly over the deeper parts of the river-bed, but again 

 rises angrily as soon as a more shallow bottom arrests its 

 triumphant career. 



Our knowledge of the courses of most of the tributaries of the 

 Amazons is very imperfect, and science knows next to nothing of 

 the natural history of their banks. Even a correct map of the 

 main stream is still wanting, for though its general course and 

 the most important bends are tolerably well laid down, the 

 numerous islands and parallel channels, the great lakes and 

 offsets, the deep bays and the varying widths of the stream are 

 quite unknown. 



The numerous tributary streams of the Amazons differ re- 

 markably in the colour of their waters and may be divided into 

 three groups — the white or pale yellowish-water rivers, the 

 blue-water rivers and the black-water rivers. 



The difference of colour between the white-water and blue- 

 water rivers is evidently owing to the nature of the country 

 they flow through ; a rocky and sandy district will always have 

 clear-water rivers; an alluvial or clayey one will have troubled 

 streams. 



The Eio Negro is the largest and most celebrated of the black- 

 water rivers. All its upper tributaries, the smaller ones especi- 

 ally, are very dark, and, when they run over white sand, give it 

 the appearance of gold, from the rich colour of the water, which, 

 when deep, appears inky black. In the rainy season, when the 

 dark clouds above cause the water to appear of a yet more 

 funereal blackness and the rising waves break in white foam over 

 the vast expanse, the scene, as may well be imagined, is gloomy 

 in the extreme. 



The peculiar colour of the black-water rivers appears 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 



