A river in S. America and the largest on the globe, its basin nearly equal in extent to the whole of Europe; traverses the continent at its greatest breadth, rises in the Andes about 50 m. from the Pacific, and after a course of 4000 m. falls by a delta into the Atlantic, its waters increased by an immense number of tributaries, 20 of which are above 1000 m. in length, one 2000 m., its mouth 200 m. wide; its current affects the ocean 150 m. out; is navigable 3000 m. up, and by steamers as far as the foot of the Andes.