In Cariaco we found most of the inhabitants in their hammocks, ill with intermittent fevers that in autumn become malignant and lead to dysentery. If you think how extraordinarily fertile and humid the plain is, and of the amount of vegetation that rots there, it is easy to understand why the atmosphere here is not as healthy as it is at Cumanà. In the torrid zone the amazing fertility of the soil, the frequent and prolonged rainy season, and the extraordinary opulence of the vegetation are advantages outweighed by a climate dangerous for whites.

During the night we had left the Orinoco waters almost without realizing it. At sunrise we found ourselves in a new country, on the banks of a river whose name we had hardly heard mentioned, and which would lead us after a foot journey over Pimichín to the Río Negro on the Brazilian frontier. The father superior of the San Fernando mission said to us: 'First you must go up the Atabapo, then the Temi, and finally the Tuamini. If the black-water current is too strong to do this the guides will take you over flooded land through the jungle. In that deserted zone between the Orinoco and the Río Negro you will meet only two monks established there. In Javita you will find people to carry your canoe over land in four days to Caìo Pimichín. If the canoe is not wrecked go straight down the Río Negro to the fort of San Carlos, then go up the Casiquiare and in a month you will reach San Fernando along the Upper Orinoco. That was the plan drawn up for us, which we carried out, without danger, in thirty-three days. The bends are such in this labyrinth of rivers that without the map which I have drawn it would be impossible to picture the route we took. In the first part of this journey from east to west you find the famous bifurcations that have given rise to so many disputes, and whose location I was the first to establish through astronomic observations. One arm of the Orinoco, the Casiquiare (108) running north to south, pours into the Guainia or Río Negro, which in turn joins the Maraìon or Amazon.

The jungle that covers the steep slope of the Santa María mountain is one of the densest I have ever seen. The trees are amazingly tall and thick. Under the dark green and matted canopy of leaves it always seems far darker than under our pine, oak and beech woods. Despite the temperature, it would seem that the air cannot absorb all the water emanating from the ground, the leaves and trunks of the trees with their tangle of orchids, peperomias and other succulent plants.

There are moments in life when it is useless to call on reason. I was very scared. However, I was sufficiently in control of myself to remember what the Indians had advised us to do in such circumstances. I carried on walking, without breaking into a run or moving my arms, and thought I noted that the wild beast had its eye on a herd of capybaras swimming in the river. The further away I got the more I quickened my pace. I was so tempted to turn round and see if the cat was chasing me! Luckily I resisted this impulse, and the tiger remained lying down. These enormous cats with spotted skins are so well fed in this country well stocked with capybara, peccaries and deer that they rarely attack humans. I reached the launch panting and told my adventure story to the Indians, who did not give it much importance.

The Cumanacoa plains, scattered with farms and tobacco plantations, are surrounded by mountains, which are higher in the south. Everything suggests that the valley is an ancient seabed. The mountains that once formed its shores rise vertically from the sea. When excavating foundations near Cumanacoa, beds of round pebbles mixed with small bivalve shells were found. According to many reliable people two enormous femur bones were discovered, about thirty years ago. The Indians took them, as do people today in Europe, for giant's bones, while the semi-educated country people, who try to explain everything, seriously claimed that they are nature's sports, not worthy of consideration. They were probably the gigantic femur of elephants of a vanished species.

May 5th. We set off on foot following our boat, which had reached Caìo Pimichín by portage. We had to wade through numerous streams. This journey demands caution because water snakes teem in the marshes. Indians pointed out tracks in the wet clay left by the small black bears that are so common on the Temi banks. They are different in size from the Ursus americanus: missionaries call them oso carnicero to differentiate them from the oso palmero or tamanoir Myrmecophaga jubata) and the oso hormiguero or tamandua ant-eater. Two of these animals, which are good to eat, defend themselves by rising up on to their hind legs. Buffon's tamanoir is called uaraca by the Indians: they are irascible and brave, which is strange given that they are without teeth. As we advanced we came across some accessible clearings in the jungle. We picked new species of coffea, a Galega piscatorum, which Indians use like the jacquinia, and a composite plant of the Temi river, as a kind of barbasco to stun fish; and a large liana known locally as bejuco de mavacure, which gives the famous curare poison.

May 10th. Overnight our canoe was loaded and we set off a little before dawn to go up the Río Negro to the mouth of the Casiquiare and begin our researches on the true course of this river linking the Orinoco and Amazon. The morning was beautiful, but as the heat rose the sky began to cloud over. The air is so saturated with water in these forests that water bubbles become visible at the slightest increase of evaporation on the earth's surface. As there is no breeze the humid strata are not replaced and renewed by drier air. This clouded sky made us gloomier and gloomier. Through this humidity Bonpland -lost the plants he had collected; for my part I feared finding the same Río Negro mists in the Casiquiare valley. For more than half a century nobody in the missions has doubted the existence of communications between the two great river systems: the important aim of our journey was reduced to fixing the course of the Casiquiare by astronomic means, especially at its point of entry into the Río Negro, and its bifurcation with the Orinoco. Without sun or stars this aim would have been frustrated, and we would have been uselessly exposed to long, weary deprivation. Our travelling companions wanted to return by the shortest journey, along the Pimichín and its small rivers; but Bonpland preferred, like myself, to persist in the original plan we had traced out while crossing the Great Cataracts. We had already traveled by canoe from San Fernando de Apure to San Carlos along the Apure, Orinoco, Atabapo, Temi, Tuamini and Río Negro for over 180 leagues. In entering the Orinoco by the Casiquiare we still had some 320 leagues to cover from San Carlos to Angostura. It would have been a shame to let ourselves be discouraged by the fear of a cloudy sky and the Casiquiare mosquitoes. Our Indian pilot, who had recently visited Mandavaca, promised us sun and 'those great stars that eat up clouds' once we had left the black waters of the Guaviare. So we managed to carry out our first plan and returned to San Fernando along the Casiquiare. Luckily for our researches the Indian's prediction was fulfilled. The white waters brought us a clear sky, stars, mosquitoes and crocodiles.