350 A JOURNEY IN BRAZIL. 
/ 
its southernmost limit during our summer months. In con- 
sequence of this, the bottom of the valley is constantly shift- 
ing, and there is a tendency to form channels from the main 
river to its tributaries, such as we have seen to exist be- 
tween the Solimoens and the Rio Negro, such as Hum- 
boldt mentions between the Hyapura and the Amazons. In- 
deed, all these rivers are bound together by an extraordi- 
nary network of channels, forming a succession of natural 
highways which will always make artificial roads, to a great 
degree, unnecessary. Whenever the country is settled, it 
will be possible to pass from the Purus, for instance, to the 
Madeira, from the Madeira to the Tapajoz, from the Tapajoz 
to the Xingu, and thence to the Tocantins, without entering 
the course of the main river. The Indians call these passes 
'furoj literally, a bore, a passage pierced from one river 
to another. Hereafter, when the interests of commerce 
claim this fertile, overflowed region, these channels will be 
of immense advantage for intercommunication." 
