46 ANNALS NEW YORK ACADEMY OF SCIENCES 



bases of the remains of the Piano Alto. These swamps are entirely due 

 to unequal erosion and a consequent deposition of sediment at different 

 levels, and this has been assisted by the growth of a dense flora and 

 changes in the channels of the rivers. The Concepcion Lake of Bolivia 

 and the Uberava Lake of Eio Paraguay and a countless number of other 

 lakes which are found within the limits of the Piano Alto (cf. Plate XII) 

 belong to this class of swamps. The swamps in the central courses of the 

 rivers are usually due to changes in their channels. 



During the rainy season, all of these swamps become flooded, and con- 

 sequently it takes about a month of heavy rains to start a large flood in 

 the lower courses of the rivers. It also takes three or four months of the 

 dry seasons before the water can percolate through the swampy vegetation 

 and get into the channels of the rivers. 



The location and heights of the waterfalls, the location and kind of 

 swamps and the kinds of environment are directly associated with the 

 geological structure and the altitudes. Inasmuch as I have already briefly 

 considered the geology, the altitudes may be profitably considered at this, 

 point. 



The highest point in Brazil is Pico de Itatiaya (2804 meters), which is 

 between the states of Eio de Janeiro and Minas Geraes. The highest 

 point in Guiana is 2621 meters. The highest point in the Cordoba Sierra 

 is 2530 meters. A few peaks of the Andes surpass 20,000 feet, and Acon- 

 cagua is over 22,000 feet high. The Piano Alto is seldom over 1000 

 meters, but one point in Goyaz is said to be 1500 meters above sea level. 

 In Eio Grande do Sul,, parts of the eroded Piano Alto are often not more 

 than 300 meters above sea level. 



The divides formed by these higher elevations are, as has been previ- 

 ously stated, correlated with the natural conditions of the descending 

 rivers. Therefore, the following brief list of altitudes along the more 

 important rivers has been given, not only on account of the above reason,, 

 but also because the abundance and the distribution of all plants and 

 animals are confined between more or less definite positive and negative 

 altitudes of the land and the sea. 



Place Altitude 



above sea level! 



Sao Antonnio, last fall in Rio Madeira 96 meters- 



Guaja Mirim, first large fall in Rio Mamore 208 



Jatoba, above the Paulo Affonso Falls 246 



Alto do Serra, near Sao Paulo 837 



Rio Tiete, near Sao Paulo about . . 750 



Jalapao, headwaters of Rio Sapao about. . 600 



Mouth of Rio Jauru in Rio Paraguay 153 



Sao Carlos, on Rio Negro above Manaos , 247 



Villa de Matto-Grosso, on Rio Guapore about. . 300 



