The old notion was, that nearly all the rivers south of Mendoza uniting in one wide stream, to which the Diamante, as one of the principal affluents, gave its name, ran direct south into the Rio Negro; and this, as I have mentioned in the preceding chapter, was Villariño's idea, and led him, without hesitation, to believe that the great river, whose mouth he explored, and which, he says, he does not doubt would have led him to Mendoza, was the Diamante. From a careful examination of Cruz's journal, and other data in my possession, I am satisfied this will be found to be an error, and that the great river which flows into the Negro is the Neuquen, which Cruz crossed on the sixth day after he left Antuco, at the place called Butacura, and about eighteen leagues on his journey. The Neuquen[30] is formed by many streams from that part of the Cordillera, all which Cruz names, and the principal of which appear to be the Rinqui-leubú, which descends from the mountain of Pichachen, and further north the Cudi-leubú, the drain of many small rivers. No one, he says, doubts that the Neuquen, from the junction of the Cudi-leubú, is navigable as far as the Rio Negro, and thence to the ocean. Proceeding in a north-easterly direction, Cruz fell in with another, considerable river, as large, he says, as the Neuquen, called by the Indians the Cobu-leubú,[31] whose sources they reported to be in the Cordillera of Curriliquin, over-against the province of Maule, in Chile; and they spoke of seven rivers which fell into it in its course from the north to the place where the expedition crossed it. Cruz says distinctly _it does not fall into the Neuquen_, but, changing its southerly course about where they passed it, it ran eastward, in which direction the travellers kept it in view, at times coasting it, for several days, till at a place called Puelec it again turned towards the south, taking thence, as the Indians affirmed, its course to the sea. This river, there can be no doubt whatever, is the Colorado, which falls into the sea a little to the north of the Rio Negro. The hilly ranges of the Cordillera were found to extend about ten leagues beyond the pass of the Cobu-leubú, above spoken of, after which the pampas commence, which continue unbroken to Buenos Ayres. Two days after passing Puelec, whence the river Cobu-leubú takes a southerly course, and having gone about seventy-four leagues by their daily computation from Antuco, the travellers reached the river called by the Indians _Chadi_-leubú, or the _Salt_ River (probably a continuation of the Atuel), which, uniting with the Desaguadero, or Drain of the Diamante, about five leagues below where they crossed it, discharges itself into a vast lake about ten leagues further south, called by the Indians the Urré-lauquen, or the bitter lake.