ACROSS UNKNOWN SOUTH AMERICA 
where your great-grandfather, who is now dead, came 
from.” 
That was too much for them. All had been anxious 
to make a smudge with smoke-black upon my note-book. 
Now they all refused to do any more thumb-marking and 
walked away; but I had fortunately already acquired the 
marks I needed from them. 
The Bororos, in fact, most Indian tribes of Central 
Brazil, knew nothing whatever of navigation. This was 
chiefly due to the fact that all the woods of Central Brazil 
had so high a specific gravity that not one of them would 
float. Hence the impossibility of making rafts, and the 
greatly increased difficulty in making boats. As for 
making dug-outs, the Indians had neither the patience 
nor the skill nor the tools to cut them out of solid trees. 
Moreover, there was really no reason why the Indians 
should take up navigation at all, when they could do 
very well without it. They could easily get across the 
smaller streams without boats, and they were too timid 
to go and attack inimical tribes on the opposite banks of 
unfordable rivers. Besides, the Indians were so few and 
the territory at their entire disposal so great, that there 
was no temptation for them to take up exploring, 
particularly by water. 
They were all good swimmers. When the river was 
too deep to ford, they merely swam across; or else, if the 
river were too broad and swift, they improvised a kind 
of temporary raft with fascines or bundles of dried burity 
leaves, to which they clung, and which they propelled with 
their feet. These fascines were quite sufficient to keep 
them afloat for a short time, enabling them also to convey 
a certain amount of goods across the water. 
In other countries, such as in Central Africa, among 
the Shilucks and the Nuers of the Sobat River (Sudan), 
and the natives on Lake Tchad, I have seen a similar 
method adopted in a far more perfected fashion. The 
194 
