This island[23] (the eastern extremity of which was found to be in latitude 39°) is not only one of the most remarkable features in the map of the River Negro, but is a point of great importance connected with the inroads of the Aucazes Indians into the Province of Buenos Ayres. It is here that, in their journeys from the Cordillera, they leave the course of the Negro and strike across to the River Colorado, whence their beaten track runs straight to the mountain ranges of the Ventana and Vulcan, where they pitch their tents, recruit their horses, and watch for a favourable opportunity to scour the Pampas, and carry off the cattle from the defenceless estancias on the frontiers of Buenos Ayres. Being at all times greatly encumbered with their women, children, and cattle, and having no notion of anything like a raft or canoe to facilitate the passage of the rivers they have to cross, they are obliged to resort to those points where they are fordable, and afterwards to follow such routes as will lead them by places affording sufficient pasture for the daily maintenance of their horses and cattle. Now, in their descent from the Cordillera, their only pass across the great River Neuquen is just above its junction with the Negro, the course of which they are forced afterwards to follow as far as the Choleechel, from the impracticability of the country to the north of it, and the scarcity of fresh water for their animals. The great importance, therefore, of any military post at this point, will be at once evident, and Villariño did not hesitate to give his strong opinion to his superiors, that a fort built here, with a small Spanish garrison, would be one of the most effectual checks upon these savages, and the best defence for the cattle owners of Buenos Ayres. After fifty years of further experience, this suggestion (in 1833) has been acted upon by General Rosas, the present Governor, and the Choleechel, now called Isla de Rosas, has been occupied as a military station.