When M. Bonpland and myself were returning from the banks of the Rio Negro, we ventured to pass the latter, that is the lower half, of the Raudal of Atures in our loaded canoe. We several times disembarked to climb over rocks, which, like dykes, connected one island with another. At one time the water shoots over these dykes; at another it falls into their cavities with a deafening hollow sound. In some places considerable portions of the bed of the river are perfectly dry, in consequence of the stream having opened for itself a subterranean passage. In this solitude the golden-coloured Rock Manakin (_Pipra rupicola_) builds its nest. This bird, which is as pugnacious as the East India cock, is one of the most beautiful birds of the tropics, and is remarkable for its double moveable crest of feathers with which its head is decorated. In the Raudal of Canucari the dyke is formed of piled-up granitic boulders. We crept into the interior of a cavern, whose humid walls were covered with confervæ and phosphorescent Byssus. The river rushed over our heads with a terrible and stunning noise. By accident we had an opportunity of contemplating this grand scene longer than we desired. The Indian boatmen had left us in the middle of the cataract, to take the canoe round a small island, at the other extremity of which, after a considerable circuit, we were to re-embark. For an hour and a half we remained exposed to a fearful thunder-storm. Night was approaching, and we in vain sought shelter in the fissures of the rocks. The little apes which we had carried with us for months in wicker cages, attracted by their plaintive cries large crocodiles, whose size and leaden-grey colour indicated their great age. I should not have alluded to the appearance of these animals in the Orinoco, where they are of such common occurrence, were it not that the natives had assured us that no crocodiles had ever been seen among the cataracts; indeed, on the strength of that assertion, we had repeatedly ventured to bathe in this portion of the river. Meanwhile our anxiety increased every moment, lest, drenched as we were and deafened by the thundering roar of the falling waters, we should be compelled to spend the long tropical night in the midst of the Raudal. At length, however, the Indians made their appearance with our canoe. Their delay had been occasioned by the inaccessibility of the steps they had to descend, owing to the low state of the water; which had obliged them to seek in the labyrinth of channels a more practicable passage.