THE RIVER OF DOUBT 277 



kind of projection that appears on the maps of this region 

 as a sierra. Probably it sent low spurs to the west, and the 

 farthest points of these spurs now and then caused rapids 

 in our course (for the rapids generally came where there 

 were hills) and for the moment deflected the river west- 

 ward from its general down-hill trend to the north. There 

 was no longer any question that the Duvida was a big 

 river, a river of real importance. It was not a minor afflu- 

 ent of some other affluent. But we were still wholly in the 

 dark as to where it came out. It was still possible, although 

 exceedingly improbable, that it entered the Gy-Parana, as 

 another river of substantially the same size, near its mouth. 

 It was much more likely, but not probable, that it entered 

 the Tapajos. It was probable, although far from certain, 

 that it entered the Madeira low down, near its point of 

 junction with the Amazon. In this event it was likely, 

 although again far from certain, that its mouth would 

 prove to be the Aripuanan. The Aripuanan does not ap- 

 pear on the maps as a river of any size; on a good stand- 

 ard map of South America which I had with me its name 

 does not appear at all, although a dotted indication of a 

 small river or creek at about the right place probably rep- 

 resents it. Nevertheless, from the report of one of his 

 lieutenants who had examined its mouth, and from the 

 stories of the rubber-gatherers, or seringuerros, Colonel 

 Rondon had come to the conclusion that this was the larg- 

 est affluent of the Madeira, with such a body of water that 

 it must have a big drainage basin. He thought that the 

 Duvida was probably one of its head streams although 

 every existing map represented the lay of the land to be 

 such as to render impossible the existence of such a river 



