HAS EM AN, GEOGRAPHICAL D I ST RIB UTION IN SOUTH AMERICA 45 



of Kio Tocantins, Forto Principe da Beira of Eio Guapore, Avanhandava 

 and Itapura of Eio Tiete, Salto Grande da Paranaponema of Eio Parana- 

 ponema, Urubupunga and Dorado of Alto Bio Parana, Itaituba of Bio 

 Tapajos, etc., are typical examples of such falls, the general location of 

 which are shown on Bartholomew's New Commercial Map of South 

 America. 



In the headwaters of practically all of the highland rivers flowing 

 into either the Amazon or the La Plata, there exist and have existed in 

 some part of their courses many very high waterfalls which are now, and 

 their ancient locations far away from their present sites have been since 

 the early Mesozoic epoch, effective barriers to the migration of all aquatic 

 forms, excepting the common highland fauna, which is always very poor 

 in species. These fails are even now, after ages of erosion, often 400 or 

 more feet high and are nearly always perpendicular. Their volume of 

 water is small and no possible side channels exist. The Kaieteur Falls 

 in Guiana, Salto cle Bio dos Patos in Parana, Brazil, the fall in Bio , 

 Santa Bita from Serra da Agoaphey and the fall in Bio Juruena of Bio 

 Tapajos are typical examples of such falls. 



Between the waterfalls of the central and lower courses of the rivers 

 and the waterfalls in their headwaters, as well as below the waterfalls in 

 the central and lower courses of the rivers and along the Atlantic coast 

 of South America, are many extensive swamps which have been produced 

 in various ways. It is these swamps which are responsible for a common 

 erroneous opinion that the most of South America consists of swampy 

 sultry lowlands which are beladen with every bad thing that exists. 

 Even though these swamps are not as extensive as they are generally 

 considered to be, they are nevertheless of profound significance, espe- 

 cially in the study of environment and the distribution of aquatic forms, 

 and therefore we will next consider the mode of origin of these swamps, 

 which may be roughly divided into two classes, as follows : 



1. The coastal swamps, which have been formed by the comparatively 

 recent slight rise of the coast, followed by an unequal deposition of sedi- 

 ment both by the rivers and by the production of sand-dunes. This is 

 true for the Lagoa dos Patos of Bio Grande do Sul, as well as for the 

 various other coastal swamps like those of Iguape and at the mouth of 

 Bio Doce. There appears to be little or no doubt that the swamps of at 

 least part of the Gran Chaco of Argentina and southwestern Paraguay, as 

 well as those at the mouth of the Amazon and Orinoco, have had a similar 

 origin. 



2. In contrast to the above type of swamps are those along the central 

 and upper courses of Bio Paraguay, known as Pantanals, and Bio Ama- 

 zonas and all of its highland affluents, as well as all the swamps along the 



