They arrived at the junction of the River Negro. This is one of the largest of the tributaries of the Amazon, and derives its name from the blackness of its waters. When taken up in a tumbler, the water is a light-red color, like a pale juniper-water, and is probably colored by some such berry. This river, opposite the town of Barra, is about a mile and a half wide, and very beautiful. It is navigable for almost any draughts to the Masaya, a distance of about four hundred miles: there the rapids commence, and the farther ascent must be made in boats. By this river, a communication exists with the Orinoco, by means of a remarkable stream, the Cassaquiare, which seems to have been formed for the sole purpose of connecting these two majestic rivers, and the future dwellers upon them, in the bonds of perpetual union. Humboldt, the great traveller and philosopher, thus speaks of it, "The Cassaquiare, as broad as the Rhine, and whose course is one hundred and eighty miles in length, will not much longer form in vain a navigable canal between two basins of rivers which have a surface of one hundred and ninety thousand square leagues. The grain of New Grenada will be carried to the banks of the Rio Negro; boats will descend from the sources of the Napo and the Ucayali, from the Andes of Quito and Upper Peru, to the mouths of the Orinoco. A country nine or ten times larger than Spain, and enriched with the most varied productions, is accessible in every direction by the medium of the natural canal of the Cassaquiare and the bifurcation of the rivers." The greatest of all the tributaries of the Amazon is the Madeira, whose junction our travellers next reached. For four hundred and fifty miles from its mouth, there is good navigation: then occur cascades, which are navigable only for boats, and occupy three hundred and fifty miles, above which the river is navigable for large vessels, by its great tributaries, into Bolivia and Brazil.