THE AMAZON DISTRICT. 327 



that, supposing the animal productions to have been originally 

 distinct, they could not well have become intermixed. 



In each of these countries we find well-marked smaller 

 districts, appearing to depend upon climate. The tropical and 

 temperate parts of America and Africa have, generally speaking, 

 distinct animals in each of them. 



On a more minute acquaintance with the animals of any 

 country, we shall find that they are broken up into yet smaller 

 local groups, and that almost every district has peculiar animals 

 found nowhere else. Great mountain-chains are found to 

 separate countries possessing very distinct sets of animals. 

 Those of the east and west of the Andes differ very remarkably. 

 The Rocky Mountains also separate two distinct zoological 

 districts ; California and Oregon on the one side, possessing 

 plants, birds, and insects, not found in any part of North 

 America east of that range. 



But there must be many other kinds of boundaries besides 

 these, which, independently of climate, limit the range of 

 animals. Places not more than fifty or a hundred miles apart 

 often have species of insects and birds at the one, which are 

 not found at the other. There must be some boundary which 

 determines the range of each species ; some external peculiarity 

 to mark the line which each one does not pass. 



These boundaries do not always form a barrier to the 

 progress of the animal, for many birds have a limited range, 

 in a country where there is nothing to prevent them flying in 

 every direction, — as in the case of the nightingale, which is 

 quite unknown in some of our western counties. Rivers 

 generally do not determine the distribution of species, because, 

 when small, there are few animals which cannot pass them ; 

 but in very large rivers the case is different, and they will, it is 

 believed, be found to be the limits, determining the range of 

 many animals of all orders. 



With regard to the Amazon, and its larger tributaries, I 

 have ascertained this to be the case, and shall here mention 

 the facts which tend to prove it. 



On the north side of the Amazon, and the east of the Rio 

 Negro, are found the following three species of monkeys, 

 Ateles paniscus, Brachiums satanas, zxidjacchus bicolor. These 

 are all found close up to the margins of the Rio Negro and 

 Amazon, but never on the opposite banks of either river ; nor 



