Madeira
the great affluent of the Amazon, having its origin in the confluence of the Mamoré and Guaporé, at about lat. 12° S., the Beni joining 110 miles lower down, and then flowing N.
E. to the Amazon, its drainage basin embracing about 425,000 square miles.
From its mouth to its first falls the distance is 578 miles; above this point navigation is broken by a series of 19 falls, rapids, and cataracts for a distance of 230 miles. Its chief tributary is the Rio Teodoro, formerly Rio Duvida (River of Doubt), explored in 1914 by Theodore Roosevelt, and re-named by Brazil in his honor.