290 PHYSICAL GEOGRAPHY OF 



forest ends, it is not more than a hundred yards wide ; whereas 

 the Uaupe's, at the furthest point the traders have reached, 

 is still a large river, from a quarter of a mile to a mile in width. 

 The Amazon and all its branches are subject, like most 

 tropical rivers, to an annual rise and fall of great regularity. 

 In the main stream, and in all the branches which flow from 

 the Andes, the waters begin to rise in December or January, 

 when the rains generally commence, and continue rising till 

 June, when the fine weather has just set in. The time when 

 the waters begin to fall is about the 2ist of June, seldom 

 deviating more than a few days from this date. In branches 

 which have their sources in a different direction, such as the 

 Rio Negro, the time of rising does not coincide. On that 

 river the rains do not commence steadily till February or 

 March, when the river rises with very great rapidity, and generally 

 is quite filled by June, and then begins to fall with the Amazon. 

 It thus happens that in the months of January and February, 

 when the Amazon is rising rapidly, the Rio Negro is still falling 

 in its upper part ; the waters of the Amazon therefore flow 

 into the mouth of the Rio Negro, causing that river to remain 

 stagnant like a lake, or even occasionally to flow back towards 

 its source. The total rise of the Amazon between high and 

 low water mark has not been accurately ascertained, as it 

 cannot be properly determined without a spirit-level ; it is, 

 however, certainly not less than forty, and probably often fifty 

 feet. If therefore we consider the enormous water surface 

 raised fifty feet annually, we shall gain from another point of 

 view an idea of the immense quantity of water falling annually 

 in the Amazon valley. We cannot take the length of the 

 Amazon with its main tributaries at less than ten thousand 

 miles, and their average width about two miles ; so that there 

 will be a surface of twenty thousand square miles of water, 

 raised fifty feet every year. But it is not only this surface that 

 is raised, for a great extent of land on the banks of all the 

 rivers is flooded to a great depth at every time of high water. 

 These flooded lands are called, in the language of the country, 

 "gapo," and are one of the most singular features of the 

 Amazon. Sometimes on one side, sometimes on both, to a 

 distance of twenty or thirty miles from the main river, these 

 gapos extend on the Amazon, and on portions of all its great 

 branches. They are all covered with a dense virgin forest of 



