Sometimes, too, the destroying pororocca--a vast wave rising across the
whole width of the stream, to the height of twelve or fifteen feet--
sweeps up the stream. Advancing noiselessly over the deeper portions of
the river-bed, it rises into an angry billow, with a fearful roar when
passing over a shallow, or meeting any impediment in its course. A
French traveller describes an island where he and his companions had
rested on their voyage down the stream. They had happily gone over to
the mainland on the previous evening, when, as they stood on the shore,
the pororocca was heard approaching. Onward it came till the island was
reached, when, with an angry roar, it burst into masses of foam, and
swept over the devoted spot, carrying in its fierce embrace not only the
whole mass of vegetation, but overturning the foundations of the island
itself, so that in a few seconds not a vestige remained. Sometimes,
too, the higher banks of the Upper Amazon, crowned by lofty trees, are
worn away by the rapid current, increased during the rainy season,
continually passing beneath them, till the upper portions, deprived of
their support, fall over with a terrific roar into the stream, dragging
with them their neighbours. The earth trembles with the concussion, the
waters hiss and foam and rush furiously over the impediments in their
course. Sometimes miles of the bank thus give way, the sound being
heard far up and down the stream. Occasionally a canoe and its crew--
who, to avoid the current, have been toiling close along the bank--have
been thus overwhelmed; while others, descending, unaware of the
obstruction, have been dragged by the furious whirlpool thus formed amid
the tangled branches, and destroyed.