DOWN AN UNKNOWN RIVER 317 



lutely unknown ground; we had seen no human being, al- 

 though we had twice heard Indians. Six weeks had been 

 spent in steadily slogging our way down through the in- 

 terminable series of rapids. It was astonishing before, 

 when we were on a river of about the size of the upper 

 Rhine or Elbe, to realize that no geographer had any idea 

 of its existence. But, after all, no civilized man of any 

 grade had ever been on it. Here, however, was a river 

 with people dwelling along the banks, some of whom had 

 lived in the neighborhood for eight or ten years; and yet on 

 no standard map was there a hint of the river's existence. 

 We were putting on the map a river, running through 

 between five and six degrees of latitude of between seven 

 and eight if, as should properly be done, the lower Aripu- 

 anan is included as part of it of which no geographer, in 

 any map published in Europe, or the United States, or 

 Brazil, had even admitted the possibility of the existence; 

 for the place actually occupied by it was filled, on the maps, 

 by other imaginary streams, or by mountain ranges. 

 Before we started, the Amazonas Boundary Commission 

 had come up the lower Aripuanan and then the eastern 

 branch, or upper Aripuanan, to 8 48', following the course 

 which for a couple of decades had been followed by the 

 rubber-men, but not going as high. An employee, either of 

 this commission or of one of the big rubber-men, had been 

 up the Castanho, which is easy of ascent in its lower 

 course, to about the same latitude, not going nearly as 

 high as the rubber-men had gone; this we found out while 

 we ourselves were descending the lower Castanho. The 

 lower main stream, and the lower portion of its main afflu- 

 ent, the Castanho, had been commercial highways for 



