HASEMAN, GEOGRAPHICAL D I ST RIB VTION IN SOUTH AMERICA 43 



than nearly all if not all of the fishes which are found in the Rio Sao 

 Francisco. Therefore, Paulo Affonso appears not to have been a barrier 

 to the migration of fishes. 



In violent contrast to Paulo Affonso are the Iguassu Palls of Eio 

 Iguassu. I say violent contrast, because the Eio Iguassu flows from the 

 sandy highlands of Parana, Brazil, and after rushing over the Parana 

 trap rock at several lesser waterfalls, finally tumbles over the Iguassu 

 Falls and flows calmly toward the sea. The Iguassu Falls are about 200 

 feet high, and even though they are not exactly perpendicular, there are 

 no side channels which could have been passed by fishes. The average 

 volume of water is about one third more than that of Niagara Falls. 



The Iguassu Falls tumble over the "Parana trap," which has been de- 

 termined as Triassic by Professor Derbj^, and they are so old that they 

 appear to have been an absolute barrier to the migration of the fishes. 

 Above the falls, I found only about 25 species of small, common highland 

 genera, many of which are slightly different from the same species in the 

 neighboring highland streams. These differences, for all we know, may 

 or may not be inherited, because the external conditions in the Eio 

 Iguassu basin are different from those in the neighboring rivers. At any 

 rate, the Iguassii Falls have been a permanent barrier to the migration of 

 lowland fishes and the deplorably poor ichthyological fauna has for the 

 most part evolved from the common highland fauna, which will be con- 

 sidered in the last part of this paper. 



The next great South American waterfall which will be briefly con- 

 sidered is that of "Sete Quedras" (Brazilian) or "Guayra" (Guarani). 

 The Guayra Falls are in the middle course of Eio Parana, between the 

 State of Parana, Brazil, and the Eepublic of Paraguay. The Parana 

 Eiver above the falls is 4200 meters wide, and the- water rushes through 

 seven channels over seven falls of varying height and width. The water 

 then unites in a narrow gorge, which is only 80 meters wide, and rushes 

 madly, with a deafening roar, for about 40 miles before its force is spent, 

 and then Eio Parana calmly rolls on toward the sea. A small Argentine 

 man-of-war went up the Parana as far as the mouth of the Iguassu Eiver, 

 which is several miles below the Guayra Falls, and sailed up the Iguassii 

 Eiver as far as the Iguassii Falls. Hence these rivers are not as impass- 

 able as many are inclined to believe. At any rate, fishes can and have 

 passed the Guayra Falls, because I found that the ichthyological fauna 

 which lives in such rivers as the Alto Parana and its affluents is identical 

 above and below the falls. 



The Pirapora Falls of the Alto Eio Sao Francisco have been errone- 

 ously stated to be a barrier to the migration of fishes. In fact, the Pira- 



