VALLEY OF THE AMAZON. 301 



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 plum- 

 met h?^ ^Hherto sounded the depth of its bed at this point, 

 the force 01 , ^tream probably rendering the operation al- 

 most impracticable. 



Its last two great tributaries are the Tapajos, six times the 

 length of the Thames, and the Xingu, twice that of the Rhine ; 

 while further east a narrow channel unites it with the River 

 Para, into which flows the broad stream of the Tocantins. 

 This river, rising in the Minas-Geraes, six hundred miles from 

 Rio Janeiro, is one thousand six hundred miles long, and ten 

 miles wide at its mouth. Opposite to Para is the large island 

 of Marajo ; and if Professor Agassiz is right in supposing that 

 the continent once extended much further to the east than it 

 now does, this island may properly be considered in the centre 

 of the mouth of the river, and the River Para might then 

 properly be called one of its true embouchures. But only a 

 few of the streams which feed the Amazon have been named. 

 Numberless other rivers swell its waters, united to it by 

 countless channels which form a wonderful network through- 

 out the whole region, joining also many of the main rivers 



