HAS EM AN, GEOGRAPHICAL DISTRIBUTION IN SOUTH AMERICA 47 



The above brief list of altitudes is sufficient to show 



1. That the upper courses of the highland rivers are at least 150 meters 

 and usually more than 200 meters above sea level. In the upper courses,. 

 I do not include the headwaters which naturally correspond more or less 

 with the altitudes of the divides. In this list, it is important to note that 

 Eio Paraguay has about the same altitudes as Eio Amazonas and stands 

 in marked contrast with that of the Alto Eio Parana and its affluents like 

 Eio Tiete. 



2. That the headwaters are rarely less than 300 meters* and on the 

 average are about 900 meters above sea level. 



3. That the middle and lower courses of the rivers are usually less than 

 200 meters and on an average are 100 meters above the sea level. The 

 main stem of the Amazon and La Plata rivers are exceptions to this rule* 

 because their middle courses are only about 100 feet above sea level. 



The marked differences in altitude, which are more or less associated! 

 with the direction of the wind, the temperature, the amount and time of 

 rainfall, the geological structure and all the other factors which compose 

 an environment, separate South America into several distinct faunal and 

 floral regions, even though most of it is generally considered to be tropical. 



Space will not permit a detailed consideration of the composition of 

 faunal regions, but perhaps the following rough analogy will make the 

 idea clear. When the naturalist who is familiar with the United States 

 thinks of the regions near Tampa, New Orleans, New York, Chicago,, 

 Flagstaff and San Francisco, he can easily distinguish any one of the 

 regions from the others in various ways. In like manner, the naturalist 

 who is familiar with South America can at once distinguish any one of 

 the following regions from the others : The Pampas, the Campos, the 

 Piano Alto, Patagonia, Gran Chacos, Mattos Crossos, the Secca or arid 

 regions of Brazil and the Cordillera de los Andes. 



In brief, when I think of Patagonia, I think of a region covered with 

 calafate bushes, low, level or rolling, scanty rainfall, temperate climate, 

 and a region characterized by a general paucity of life, but not a desert. 

 When I think of Pampas, I think of a deep, rich alluvial soil, whose 

 grassy surface is as level as a floor and in many ways is like an Illinois 

 prairie which never freezes. When I think of the Piano Alto and Campos, 

 I think of more or less elevated sandy plains which are covered with 

 scanty highland grasses, an occasional scrubby tree, sparkling water, few 

 pests and a delightful climate. When I think of Chacos, I think of 

 swamp palms, Lepidosiren, cutting grasses, floating treacherous grassy 

 surfaces, decaying plants, foul odors, sultry atmosphere and alligators. 

 When I think of the vast Secca country of northeastern Brazil, I think 



