The Ventuari is the largest Venezuelan tributary of the Upper Orinoco, yet the three hundred miles or so of its course are practically unknown to Europeans. As far as its valley has been explored, alternating forests and savannahs have been found. Across these in colonial times there was once a track uniting Esmeralda directly with the Lower Orinoco by way of the Caura; the route lay up the Padamo and then across the head-waters of the Ventuari to the source of the Erewato, a tributary of the Caura. Along this road there was a chain of forts, but the cruelties of the soldiers at last led the Indians to unite for their examination, and Humboldt tells us that every man in the fifty-league-long chain of forts was slain one night in 1776. The Indians told him that by this road it was ten days from Esmeralda to the headquarters of the Ventuari, and two days thence to the mouth of the Erewato. Some of the upland savannahs which this road crossed must be excellently situated both for occupation by Europeans and for stock-raising, but the region is naturally very difficult of access at present, lying as it does in the very back of the hinterland of the Guayana. These districts are occupied by the Maquiritare, near relatives of, if not identical with, the Waiomgomo of the Caura. Their territory produces rubber and timber as well as gold. Auriferous quartz is said to have been seen by casual traders up the Ventuari, and the inhabitants collect the precious metal, storing it in jars, with which, by devious waterways and many portages, they travel across to British Guiana to trade for rifles of a quality unobtainable in southern Venezuela. Separated by a narrow ridge from the Ventuari is the upper valley of the Merevari (Caura), a practically unknown region, scantily peopled by the Waiomgomo, and apparently possessing no particular attractions from a commercial point of view. On the south side of the main river we have one of the most notable instances of a natural phenomenon peculiar to the elevated inland plain of South America in the celebrated bifurcation of the Casiquiare, some twenty miles below Esmeralda. The watershed between the Orinoco and the Rio Negro is here very ill defined, and near the bifurcation a line of slight elevation on the southern bank of the former river is all that exists to separate the two great drainage systems. At the head of the Casiquiare the elevation is sufficiently reduced to allow some part of the water of the Orinoco to overflow into the southern drainage area, and so affords a through waterway to the whole of the Amazon Valley. On the eastern side of the _Brazo_, as it is called, there are numerous tributaries, whose upper courses are absolutely unknown, save from the casual reports of wandering Indians. The main stream and its affluents alike flow through great forests, and the immediate neighbourhood of the Casiquiare being level, the valley is damp and abounds in small lakes and swamps.