The Latitude Of Mandavaca Is 2 Degrees 4 Minutes 7 Seconds; Its Longitude, According To The Chronometer, 69 Degrees 27 Minutes.

I found the magnetic dip 25.25 degrees (cent div), showing that it had increased considerably from the fort of San Carlos.

Yet the surrounding rocks are of the same granite, mixed with a little hornblende, which we had found at Javita, and which assumes a syenitic aspect. We left Mandavaca at half-past two in the morning. After six hours' voyage, we passed on the east the mouth of the Idapa, or Siapa, which rises on the mountain of Uuturan, and furnishes near its sources a portage to the Rio Mavaca, one of the tributary streams of the Orinoco. This river has white waters, and is not more than half as broad as the Pacimoni, the waters of which are black. Its upper course has been strangely misrepresented on maps. I shall have occasion hereafter to mention the hypotheses that have given rise to these errors, in speaking of the source of the Orinoco.

We stopped near the raudal of Cunuri. The noise of the little cataract augmented sensibly during the night, and our Indians asserted that it was a certain presage of rain. I recollected that the mountaineers of the Alps have great confidence in the same prognostic.* (* "It is going to rain, because we hear the murmur of the torrents nearer," say the mountaineers of the Alps, like those of the Andes. The cause of the phenomenon is a modification of the atmosphere, which has an influence at once on the sonorous and on the luminous undulations. The prognostic drawn from the increase and the intensity of sound is intimately connected with the prognostic drawn from a less extinction of light. The mountaineers predict a change of weather, when, the air being calm, the Alps covered with perpetual snow seem on a sudden to be nearer the observer, and their outlines are marked with great distinctness on the azure sky. What is it that causes the want of homogeneity in the vertical strata of the atmosphere to disappear instantaneously?) It fell before sunrise, and the araguato monkeys had warned us, by their lengthened howlings, of the approaching rain, long before the noise of the cataract increased.

On the 14th, the mosquitos, and especially the ants, drove us from the shore before two in the morning. We had hitherto been of opinion that the ants did not crawl along the cords by which the hammocks are usually suspended: whether we were correct in this supposition, or whether the ants fell on us from the tops of the trees, I cannot say; but certain it is that we had great difficulty to keep ourselves free from these troublesome insects. The river became narrower as we advanced, and the banks were so marshy, that it was not without much labour M. Bonpland could get to a Carolinea princeps loaded with large purple flowers. This tree is the most beautiful ornament of these forests, and of those of the Rio Negro. We examined repeatedly, during this day, the temperature of the Cassiquiare. The water at the surface of the river was only 24 degrees (when the air was at 25.6 degrees.) This is nearly the temperature of the Rio Negro, but four or five degrees below that of the Orinoco. After having passed on the west the mouth of the Cano Caterico, which has black waters of extraordinary transparency, we left the bed of the river, to land at an island on which the mission of Vasiva is established. The lake which surrounds this mission is a league broad, and communicates by three outlets with the Cassiquiare. The surrounding country abounds in marshes which generate fever. The lake, the waters of which appear yellow by transmitted light, is dry in the season of great heat, and the Indians themselves are unable to resist the miasmata rising from the mud. The complete absence of wind contributes to render the climate of this country more pernicious.

From the 14th to the 21st of May we slept constantly in the open air; but I cannot indicate the spots where we halted. These regions are so wild, and so little frequented, that with the exception of a few rivers, the Indians were ignorant of the names of all the objects which I set by the compass. No observation of a star helped me to fix the latitude within the space of a degree. After having passed the point where the Itinivini separates from the Cassiquiare, to take its course to the west towards the granitic hills of Daripabo, we found the marshy banks of the river covered with bamboos. These arborescent gramina rise to the height of twenty feet; their stem is constantly arched towards the summit. It is a new species of Bambusa with very broad leaves. M. Bonpland fortunately found one in flower; a circumstance I mention, because the genera Nastus and Bambusa had before been very imperfectly distinguished, and nothing is more rare in the New World, than to see these gigantic gramina in flower. N. Mutis herborised during twenty years in a country where the Bambusa guadua forms marshy forests several leagues broad, without having ever been able to procure the flowers. We sent that learned naturalist the first ears of Bambusa from the temperate valleys of Popayan. It is strange that the parts of fructification should develop themselves so rarely in a plant which is indigenous, and which vegetates with such extraordinary rigour, from the level of the sea to the height of nine hundred toises, that is, to a subalpine region the climate of which, between the tropics, resembles that of the south of Spain. The Bambusa latifolia seems to be peculiar to the basins of the Upper Orinoco, the Cassiquiare, and the Amazon; it is a social plant, like all the gramina of the family of the nastoides; but in that part of Spanish Guiana which we traversed it does not grow in those large masses which the Spanish Americans call guadales, or forests of bamboos.

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