THE AMAZON VALLEY. 
419 
rains do not commence steadily till February or March, 
when the river rises with very great rapidity, and gene- 
rally 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 ra- 
pidly, 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 smTace raised fifty feet annually, we shall gain 
from another point of view an idea of the immense quan- 
tity of water falling annually in the Amazon valley. We 
cannot take the length of the Amazon and 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 lan- 
guage 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 lofty trees, 
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