A DIABOLICAL SPOT 
We were in a region of immense volcanic domes 
composed of eroded rock, with many small perforations 
and large holes two or three feet in diameter, highly pol¬ 
ished inside as if they had been varnished. Those rocks 
were similar to those I had met in the higher part of the 
plateau of Matto Grosso. Some of the holes in the rock 
had been enlarged to a great extent by the water of the 
river revolving inside them. 
After we had passed the great whirlpool we found 
many curious mounds of sand twenty feet high among 
great masses of lava and eruptive rock. Those mounds 
were formed by musical sand such as we had met before. 
We called it in this particular place “ moaning sand,” as 
instead of whistling as usual it produced a wailing sound 
like the cry of a hungry puppy. 
On the right side of the stream we came to an im¬ 
portant tributary fifty metres wide; 500 metres lower 
down another strong rapid was reached. I was greatly 
amused to see how my men now invariably pulled up the 
canoe when we perceived a rapid and unloaded her, care¬ 
fully taking her down with ropes. One man, nevertheless, 
had to be in the canoe to steer her. Alcides always vol¬ 
unteered to take the job. 
Two hundred metres below this rapid the river turned 
a sharp corner. There we met one of the most dangerous 
rapids and whirlpools I have ever seen. It was quite awe¬ 
inspiring to look at those vicious waters, the water in the 
vortex being raised like a wall two or three feet higher 
than the greatest waves of the rapid by the force with 
which it revolved. The entire river, which, as we have 
seen, was in some places 2,000 metres wide, was now 
squeezed through a narrow cut in the hill range, two great 
arms of water joining directly above that spot. The water 
was naturally forced through that small opening at an 
incredible pace. The high vertical rocks at the side of the 
small channel which was there formed made it extremely 
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