After receiving the waters of numerous streams, many of which flow for considerable distances parallel with its shores, and are united by a network of channels, it is joined by its most considerable northern tributary--the Rio Negro. This stream, rising in the mountains of Venezuela, and passing amidst the Llanos, robbing the Orinoco of part of its waters, has already, before it reaches the Amazon, flowed for a course of one thousand five hundred miles. It is called the Negro from its black colour. It is here not less than nineteen fathoms deep, and three thousand six hundred paces broad. The next great affluent is the Yapura, which, rising in the mountains of New Granada, takes a south-easterly course for one thousand miles, its principal mouth entering the Amazon opposite the town of Ega; but it has numberless small channels, the streams of which, two hundred miles apart, flow into the great river. The upper part of the Amazon is frequently called the Solimoens, which name it retains as far south as the mouth of the River Negro. About sixty miles further east, its largest southern affluent--the gigantic Madeira--unites its milky waters with the turbid stream of the main river. One branch, the Beni, rises in the neighbourhood of the ancient Cuzco in Peru, near Lake Titicaca, its whole extent from the centre of the province of Bolivia being nearly the length of the Amazon itself. At its mouth it is two miles wide and sixty-six feet deep; and five hundred miles up it is a mile wide. Numerous islands are found in its course: for nearly five hundred miles it is navigable for large vessels, when a cataract intervenes. Were it not for this, there would be a free navigation from the centre of the province of Bolivia to the ocean, embracing islands the size of many of the Old World provinces, and widening into broad lakes. The monarch of waters flows on between its low forest-clothed banks till, four hundred miles from its mouth, it reaches the Strait of Obydos, where it is narrowed to two thousand paces. Through this channel its waters rush with immense force, calculated at five hundred thousand cubic feet in one second--sufficient to fill all the streams in Europe, and swell them to overflowing. No plummet has hitherto sounded the depth of its bed at this point, the force of the stream probably rendering the operation almost impracticable.