182 CATARACTS OF THE ORINOCO. 



Cataracts, it was striking to hear the thunder of the rushing tor- 

 rents sound three times louder by night than by day. In all Euro- 

 pean waterfalls the same phenomenon is remarked. What can be 

 its cause in a wilderness where' there is nothing to interrupt the re- 

 pose of nature? - Perhaps the currents of heated ascending air by 

 causing irregular density in the elastic medium impede the propa- 

 gation of sound during the day, by the disturbance they may occa- 

 sion in the waves of sound; whereas during the nocturnal cooling 

 of the earth's surface the upward currents cease. 



The Indians called our attention to ancient tracks of wheels. 

 They speak with admiration of the horned animals (oxen), which in 

 the times of the Jesuit missions used to draw the canoes on wheeled 

 supports, along the left bank of the Orinoco, from the mouth of the 

 Cameji to that of the Toparo. The lading was not then removed 

 from the boats, nor were the latter worn and injured as they now are 

 by being constantly stranded upon the rocks and dragged over their 

 rough surface. 



The topographical plan of the district sketched by me shows the 

 facilities which the nature of the ground offers for the opening of a 

 canal from the Cameji to the Toparo, which would form a navigable 

 side-arm to the river, the dangerous portion of which would be thus 

 avoided. I proposed its execution to the Governor-General of Vene- 

 zuela. 



The Raudal of Atures closely resembles that of Maypures; like 

 it, it is a cluster of islands between which the river forces its way 

 for ten or twelve thousand yards; a forest of palms rising from the 

 midst of the foaming waters. The most celebrated Steppes of this 

 Raudal are situated between the Islands of Avaguri and Javariveni, 

 between Suripamana and Uirapuri. 



When M. Bonpland and I returned from the banks of the Rio 

 Negro, we ventured to pass the latter or lower half of the Raudal 

 of Atures with the loaded canoe, often leaving it for the rocky dikes 

 which connect one island with another. Sometimes the waters rush 

 over these dikes, and sometimes they fall with a hollow thundering 

 sound into cavities^ and flowing for a time through subterranean 

 channels, leave large pieces of the bed of the river dry. Here the 

 golden Pipra rupicola makes its nest; it is one of the most beautiful 



