384 AMAZONIA AND LA PLATA. 



abruptly northwards to a longitudinal valley separating- tlie great Cordillera from 

 the parallel range known as the Cordillera de los Cipreses. ^Vfter receiving the 

 overflow from Lake Treful the Limay pierces this rocky barrier, beyond which it 

 is joined by the longer and equally cojjious CoUon-Ciira rising about KiO miles 

 farther north. On its winding course southwards the Collon-Cura is joined by 

 the emissary of the Alumine lagoon, which stands near the divide between the 

 Biobio and Ptio Negro, and possibly sends its overflow to both basins. 



Swollen by all the torrents from the Cordilleras, the Limay flows rapidly in a 

 north-easterly course, flanked here and there by reddish clifls, and elsewhere 

 expanding in broad depressions studded with lagoons, the resort of myriads of 

 water-fowl. The current, although very swift, nowhere develops rapids, so that a 

 steamer with powerful engines might ascend all the way to Lake Nahuel-Huapi, 

 and even penetrate into the Collon-Cura affluent. 



The Lower Rio Negro. 



At the confluence the Neuquen and the Limay have about the same mean 

 annual discharge ; bU(t the Neuquen, traversing a more arid region, presents far 

 greater discrepancies between high and low water. To judge from the disposition 

 of its valley, the Limay would seem to be the true upper branch of the Cura 

 Leofu, or E-io Negro, to which the Indians appear to have given this name, not 

 from the colour of its waters, but from the rapids and other dangerous obstructions 

 to its navigation. Flowing on a shingly or rocky bed, the stream maintains its 

 pure sea-green colour throughout the year, except for two or three days after the 

 floods, when it changes to " a dull red with the red earth that some swollen tribu- 

 iary hundreds of miles to the west has poured into its current. This change 

 lusts only a day or two, after which the river runs green and pure again." * 



Flowing in its broad, regularly inclined valley at first eastwards, then to the 

 south-east, the " Black River " receives not a single tributary from the arid Pata- 

 gonian plains. But although, under this rainless climate, it gradually loses volume 

 on its seaward course, it still maintains a mean depth of over thirteen feet. About 

 midway it breaks into two branches which ramify amid groups of shifting islands, 

 forming the Choele Choel, famed in Patagonian history as the place where the 

 native warriors crossed to swoop down on the Argentine settlements. 



The Choele Choel, some 60 miles long with a mean breadth of G or 7 miles, 

 consists of alluvial soil at a dead level clothed with bush and herbage. Right 

 and left stretch low-lying plains bounded by the scarps of the plateau (here about 

 800 feet high), and often submerged by the flood waters of the Neuquen, derived 

 in summer from the melting snows, in winter from the heavy rains on the 

 mountain slopes. The Rio Negro glides silently into the sea through a single 

 channel, without in any way modifying the trend of the shore-line. f 



* W. H. Hudson, Idle Bays in Patagonia, p. 36. 



t Length of the Rio Negro from Lake Nahuel-Huaj^i to the sea . . 575 miles 

 Area of catchment basin . . . . . . . 50,000 square miles. 



Probable discharge, according to Gruerrico . . . 14,000 cubic feet per second. 



