THE AMAZON VALLEY. 291 



lofty trees, whose stems are every year, during six months, from 

 ten to forty feet under water. In this flooded forest the Indians 

 have paths for their canoes, cutting across from one river to 

 another, which are much used, to avoid the strong current of the 

 main stream. From the mouth of the river Tapajoz to Coary, 

 on the Solimoes, a canoe can pass, without once entering the 

 Amazon : the path lies across lakes, and among narrow inland 

 channels, and through miles of dense flooded forest, crossing 

 the Madeira, the Purus, and a hundred other smaller streams. 

 All along, from the mouth of the Rio Negro to the mouth of 

 the Iga, is an immense extent of gapo, and it reaches also far up 

 into the interior ; for even near the sources of the Rio Negro, 

 and on the upper waters of the Uaupe's, are extensive tracts 

 of land which are annually overflowed. 



In the whole country around the mouth of the Amazon, 

 round the great island of Marajo, and about the mouths of 

 the Tocantfns and Xingu, the diurnal and semi-monthly tides are 

 most felt, the annual rise and fall being almost lost. Here the 

 low lands are overflowed at all the spring-tides, or every fort- 

 night, subjecting all vegetation to another peculiar set of 

 circumstances. Considerable tracts of land, still covered with 

 vegetation, are so low, that they are flooded at every high 

 water, and again vary the conditions of vegetable growth. 



GEOLOGY. 



Fully to elucidate the Geology of the Amazon valley, requires 

 much more time and research than I was able to devote to it. 

 The area is so vast, and the whole country being covered with 

 forests renders natural sections so comparatively scarce, that 

 the few distant observations one person can make will lead to 

 no definite conclusions. 



It is remarkable that I was never able to find any fossil 

 remains whatever, — not even a shell, or a fragment of fossil 

 wood, or anything that could lead to a conjecture as to the 

 state in which the valley existed at any former period. We 

 are thus unable to assign the geological age to which any of 

 the various beds of rock belong.* 



My notes, and a fine series of specimens of the rocks of the Rio 



* The sandstone rocks of Montealegre have since been ascertained to be 

 of cretaceous age. 



