I will preface my consideration of the question of the sources of the Orinoco with my own conjectures in relation to the subject. The perilous route travelled in 1739 by the surgeon Nicolas Hortsmann, of Hildesheim; in 1775 by the Spaniard Don Antonio Santos, and his friend Nicolas Rodriguez; in 1793 by the Lieutenant-Colonel of the 1st Regiment of the Line of Para, Don Francisco José Rodriguez Barata; and (according to manuscript maps, for which I am indebted to the former Portuguese Ambassador in Paris, Chevalier de Brito) by several English and Dutch settlers, who in 1811 travelled from Surinam to Para by the portage of the Rupunuri and by the Rio Branco;—divides the _terra incognita_ of the Parime into two unequal parts, and serves to mark the position of a very important point in the geography of those regions—viz., the sources of the Orinoco, which it is no longer possible to remove to an indefinite distance towards the east, without intersecting the bed of the Rio Branco, which flows from north to south through the fluvial district of the Upper Orinoco; while this portion of the great river itself pursues for the most part a direction from east to west. The Brazilians, since the beginning of the present century, have from political motives manifested a vivid interest in the extensive plains east of the Rio Branco.[IG] Owing to the position of Santa Rosa on the Uraricapara, whose course appears to have been pretty accurately determined by Portuguese engineers, the sources of the Orinoco cannot be situated east of the meridian of 63° 8′ west long. This is the eastern limit beyond which they cannot be placed, and taking into consideration the state of the river at the Raudal de los Guaharibos (above Caño Chiguire, in the country of the strikingly fair-skinned Guaycas Indians, and 52′ east of the great Cerro Duida), it appears to me probable that the Orinoco in its upper part does not extend, at the utmost, beyond the meridian of 64° 8′ west long. This point is, according to my combinations, 4° 12′ west of the little lake of Amucu, which was reached by Sir Robert Schomburgk.