In The Marshy Forest Which We Traversed, To Convey Our Canoe From The Rio Tuamini To The Cano Pimichin And The Rio Negro, Why, In The Same Soil, Did We Ford Alternately Rivulets Of Black And White Water?

Why did we find no river white near its springs, and black in the lower part of its course?

I know not whether the Rio Negro preserves its yellowish brown colour as far as its mouth, notwithstanding the great quantity of white water it receives from the Cassiquiare and the Rio Blanco.

Although, on account of the abundance of rain, vegetation is more vigorous close to the equator than eight or ten degrees north or south, it cannot be affirmed, that the rivers with black waters rise principally in the most shady and thickest forests. On the contrary, a great number of the aguas negras come from the open savannahs that extend from the Meta beyond the Guaviare towards the Caqueta. In a journey which I made with Senor Montufar from the port of Guayaquil to the Bodegas de Babaojo, at the period of the great inundations, I was struck by the analogy of colour displayed by the vast savannahs of the Invernadero del Garzal and of the Lagartero, as well as by the Rio Negro and the Atabapo. These savannahs, partly inundated during three months, are composed of paspalum, eriochloa, and several species of cyperaceae. We sailed on waters that were from four to five feet deep; their temperature was by day from 33 to 34 degrees of the centigrade thermometer; they exhaled a strong smell of sulphuretted hydrogen, to which no doubt some rotten plants of arum and heliconia, that swam on the surface of the pools, contributed. The waters of the Lagartero were of a golden yellow by transmitted, and coffee-brown by reflected light. They are no doubt coloured by a carburet of hydrogen. An analogous phenomenon is observed in the dunghill-waters prepared by our gardeners, and in the waters that issue from bogs. May we not also admit, that it is a mixture of carbon and hydrogen, an extractive vegetable matter, that colours the black rivers, the Atabapo, the Zama, the Mataveni, and the Guainia? The frequency of the equatorial rains contributes no doubt to this coloration by filtration through a thick mass of grasses. I suggest these ideas only in the form of a doubt. The colouring principle seems to be in little abundance; for I observed that the waters of the Guainia or Rio Negro, when subjected to ebullition, do not become brown like other fluids charged with carburets of hydrogen.

It is also very remarkable, that this phenomenon of black waters, which might be supposed to belong only to the low regions of the torrid zone, is found also, though rarely, on the table-lands of the Andes. The town of Cuenca in the kingdom of Quito, is surrounded by three small rivers, the Machangara, the Rio del Matadero, and the Yanuncai; of which the two former are white, and the waters of the last are black (aguas negras). These waters, like those of the Atabapo, are of a coffee-colour by reflection, and pale yellow by transmission.

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