SCHULTZENSTEIN — NUTRITIVE CONSTITUENTS OE "WATER. 115 



it must be rich in humous and extractive matter. As regards the 

 quantity of humus in river-water, we have at present only very 

 confined observations ; but little attention was given to the sub- 

 ject so long as the important agency of the quantity of humus 

 contained in water upon vegetation was unknown. It is, how- 

 ever, sometimes so great, that it communicates a yellow, or in 

 great depths a coffee- coloured, or even dark-brown tint. The 

 black streams first attracted attention in America, where the Rio 

 Negro, or Black River, derived its name from the dark colour of 

 the water, as also many tributaries of the Orinoko. The Atapabo, 

 Gruiainia, and Tuamini are of a dark coffee-brown. Lyell states, in 

 his ' Travels in North America,' that in the vast swamps in the 

 narrow atlantic plain of North America, especially in the Great 

 Dismal between Norfolk and Welden (between Virginia and North 

 Carolina), there is a lake seven miles long and five wide whose 

 waters are of a dark brown from the dissolved humus. 



The " blackwaters " (Karassu) which are often found on the 

 mountains of the East, derive their name equally from the brown 

 or black colour of their waters in consequence of the dissolved 

 humus. 



Very recently, Junghuhn, in his travels in Sumatra, directed 

 his attention to the "blackwaters." He says, "The mountain- 

 streams of the Batta land of Sumatra, especially on the tableland 

 of the provinces of Sieperok and Tobah, have a coffee-brown tint. 

 In the beds of the river shaded by forests, their water appears very 

 dark, but of a golden-yellow in a transparent glass. This tint is 

 universal in the interior of Sumatra ; but it is most striking in 

 the high tableland, where the slight inclination of the surface in 

 the dark primeval forests gives rise to frequent inundations, and 

 where, besides the vegetable substances which rot upon the moory 

 ground, a quantity of root-threads are irrigated with water, 

 which, impregnated with the extractive matter which enters into 

 their composition, forms a kind of cold infusion. The water 

 may nevertheless be drunk without injury, and is void either 

 of taste or smell." ('Travels in the Batta Land of Sumatra,' i. 

 p. 256.) 



It is rather surprising that the dark waters of Europe should 

 hitherto have been almost entirely overlooked, notwithstanding 

 their appearance in almost every river which runs down from the 

 Hartz, especially theBrocken. The water of Use, near Ilsenburg, is 

 at some deeper parts of the river almost coffee-brown. If we follow 

 the river towards the heights of the Brocken, we remark that almost 



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