The Volga is celebrated for its seventy mouths; and the Ganges, the Nile, Mississippi, and Orinoco pour out their current through several branches. The space inclosed within these various channels is called a delta, from its triangular form, and general resemblance to the shape of the Greek letter Δ. So powerfully do many of the great rivers rush into the ocean, that their waters are distinct from those of the briny deep, when out of sight of the land. A British fleet lying opposite to the mouth of the Rhone occasionally took up fresh water at a considerable distance from the shore; and Columbus found his vessel in the fresh water of the Orinoco before he discovered the continent of South America. The collision of a great river current and the opposing tide of the sea is sometimes so violent as to occasion an elevated ridge of waters, heaving and tossing in a tremendous manner, shattering to pieces the ill-fated vessel that comes into contact with it. The passage of the Garonne into the Bay of Biscay, and of the Ganges into the Bay of Bengal, exhibit this phenomenon. In treating of the magnitude of rivers, some writers refer to the elevation of the range of mountains from which they descend; and it is obviously true, that the greater the height of the mountains, the more extensive are their snows and glaciers, and the larger the supply of water furnished by springs and torrents. But the magnitude of a stream is more especially regulated by the extent of country which forms the declivities of its basin, though there is no invariable proportion here, for a small basin in a humid region will yield a greater quantity of water than one much more considerable in a different situation. High mountains, a humid climate, and a wide superficial drainage, are the three physical circumstances which lead to the accumulation of vast bodies of water, the magnitude of which will be proportionate to the degree in which these causes are in combined operation. Upon the surface of the New World, we have these causes acting with greater intensity than upon that of the Old, which explains the superior character of the streams of the western continent. The following exhibits the extent of the hydrographical regions of the principal rivers of the globe, with the proportionate quantity of their waters: