NEGRO, Rio, a large river of Patagonia, in South America. The banks of this river, as well as the numerous islands with which it is in many parts studded, are covered with low willows, from which cause it is sometimes called the Rio Sauces. Its Indian name is Cusu-Leubu, signifying Rio Negro, or the Black River, from the dark hue of its waters.^[1. This river, which forms so important a feature in the geography of that part of South America, has hitherto been laid down solely on the authority of Father Falkner’s work upon Patagonia, published in this country in the year 1775. In the year 1836', however, the Royal Geographical Society of London published a correct account and map of it, which were derived from a Journal of an Original Voyage of Discovery up the Rio Negro, performed in the years 1782-1783, by Don Basilio Villarino, who had been employed for thb purpose by the Spanish government. To these we have had recourse in drawing up the above article. ] The results of the expedition alluded to in the note were important, although not so completely satisfactory as could have been wished, as the large affluent from the north, supposed to be Diamante, was not examined. But the great point established was, that it is possible to navigate the main stream of the Rio Negro from its mouth, in the Southern Atlantic, to the very foot of the Cordillera of Chili, within fifty miles of Valdivia, upon the shores of the Pacific, a distance of about 525 miles without including the windings of the river. From its mouth in south latitude 41 β 5 f , to the great island of Choleechel or Chuelechel, in latitude 39°, its general course tends to the north-north-west, although in some parts it is exceedingly tortuous. As far as this point, the bottom of the river is sand, and the country is described as an arid sandy level, destitute of vegetation, excepting some insulated patches along the shore, which being from time to time flooded, are covered with good pasturage. The island of Choleechel, which constitutes so conspicuous a feature in the map of the river, is twenty-seven miles in length [7:16:80]and nine in width; but appears to produce nothing except pasturage. From this island to Diamante, a distance of 156 miles, the course of the river is nearly due west; its bottom is gravelly, with many pebbles, and the aspect of the country is for the most part desolate from want of vegetation. The Diamante, at its confluence with the Rio Negro, is nearly as large as the latter river; and as it appears to be the drainage of numerous streams which descend from the eastern side of the Cordillera, between the latitudes of 32° and 36°, its periodical floods must be formidable, and much greater than those of the Rio Negro. It is much intersected by small islands overgrown with stunted willows. The low lands along the shore are sterile, and all beyond a range of steep red cliffs, by which these are bounded, the country appeared totally destitute of herbage, not a tree being visible. From about the confluence of these two rivers, the Rio Negro takes a southsouth-western direction, running between high precipitous banks, where in some parts the river was not more than five hundred yards across. After these are passed, the country becomes more level, and the stream widens. Another considerable tributary, called the Pichi Epicuntu, which descends from some of the snowy peaks of the Cordillera, flows into the Negro in lat. 39° 35' S. Farther onwards the river becomes intersected by innumerable islands, extremely shallow in some parts; and the bottom is strewed with rounded stones and boulders, which increase in size as the range of the Cordillera is approached. The windings of the river also become very large, and, from flowing in a main current nearly due south, it takes a westerly direction, and then bends to the north. The farthest point reached by Villarino was in lat. 39 β 40'; and here, within fifty miles of Valdivia, his course was checked by the Indians, who appear to have been apprehensive that his expedition had for its main object the stoppage of a great pass near Choleechel, by which they were in the habit of making predatory excursions into the province of Buenos Ayres. He, in fact, points out how these marauders might be effectually kept in check by establishing a fort at the point above mentioned; and, after a lapse of fifty years, this suggestion has been carried into effect by the authorities of Buenos Ayres. In 1833 a military post was formed at the Choleechel, which will not only secure the southern parts of the republic from the hostile inroads of the Indians, but will no doubt ultimately lead to our obtaining much new and interesting information respecting a vast tract of country as yet unknown to us. The depth of the Rio Negro varies much, as well as the current, depending in some measure on the breadth of the bed of the river; and it is liable to great changes in the time of the floods, which are periodical, and twice in the year, from the rains in the winter, and the melting of the snows in summer. With regard to its breadth, nothing satisfactory can be stated, as it varies exceedingly at all times, and widens and contracts at different seasons of the year.