We were still in the Brazilian highlands.  The forest did not teem with life.  It was generally rather silent; we did not hear such a chorus of birds and mammals as we had occasionally heard even on our overland journey, when more than once we had been awakened at dawn by the howling, screaming, yelping, and chattering of monkeys, toucans, macaws, parrots, and parakeets.  There were, however, from time to time, queer sounds from the forest, and after nightfall different kinds of frogs and insects uttered strange cries and calls.  In volume and frequency these seemed to increase until midnight.  Then they died away and before dawn everything was silent.

At this camp the carregadores ants completely devoured the doctor’s undershirt, and ate holes in his mosquito-net; and they also ate the strap of Lyra’s gun-case.  The little stingless bees, of many kinds, swarmed in such multitudes, and were so persevering, that we had to wear our head-nets when we wrote or skinned specimens.

The following day was almost without rain.  It was delightful to drift and paddle slowly down the beautiful tropical river.  Until mid-afternoon the current was not very fast, and the broad, deep, placid stream bent and curved in every direction, although the general course was northwest.  The country was flat, and more of the land was under than above water.  Continually we found ourselves travelling between stretches of marshy forest where for miles the water stood or ran among the trees.  Once we passed a hillock.  We saw brilliantly colored parakeets and trogons.  At last the slow current quickened.  Faster it went, and faster, until it began to run like a mill-race, and we heard the roar of rapids ahead.  We pulled to the right bank, moored the canoes, and while most of the men pitched camp two or three of them accompanied us to examine the rapids.  We had made twenty kilometres.

We soon found that the rapids were a serious obstacle.  There were many curls, and one or two regular falls, perhaps six feet high.  It would have been impossible to run them, and they stretched for nearly a mile.  The carry, however, which led through woods and over rocks in a nearly straight line, was somewhat shorter.  It was not an easy portage over which to carry heavy loads and drag heavy dugout canoes.  At the point where the descent was steepest there were great naked flats of friable sandstone and conglomerate.  Over parts of these, where there was a surface of fine sand, there was a growth of coarse grass.  Other parts were bare and had been worn by the weather into fantastic shapes—­one projection looked like an old-fashioned beaver hat upside down.  In this place, where the naked flats of rock showed the projection of the ledge through which the river had cut its course, the torrent rushed down a deep, sheer-sided, and extremely narrow channel.  At one point it was less than two yards across, and for quite a distance not more than five or six yards.  Yet only a mile or two above the rapids the deep, placid river was at least a hundred yards wide.  It seemed extraordinary, almost impossible, that so broad a river could in so short a space of time contract its dimensions to the width of the strangled channel through which it now poured its entire volume.