Whilst the fort was building on the Tandil, communications were opened with the Indians residing near the Ventana, proposing to them to join in active operations against the Ranqueles tribes--the Spaniards thinking, as on other occasions, to invoke the tribes in war with each other, and to profit by the weakening of both parties; but the Indians were this time upon their guard. They saw clearly enough that the march of such an army into their territory could have only one object,--the forcible occupation of their lands,--and they took their measures accordingly with their usual astuteness and cunning. Assenting, apparently, to the general propositions made to them, they invited the Buenos Ayrean general to repair with his principal officers to the neighbourhood of the Ventana, there to enter into the definitive treaties. They probably hoped by some _ruse_ to get the governor himself into their hands, and were greatly disappointed at his only sending his second in command, General Rondeau, to treat with them. Rondeau marched into their territory with a force of 1000 men, passing to the west of the Tinta mountains, and, after going some distance, was met by the principal Caciques, with a large assemblage of their fighting men; and here commenced a negociation, in which the Buenos Ayrean general was fairly outwitted. The Indians, affecting distrust, proposed that some officers of consequence should be sent to them as hostages during the conferences, offering, on their part, to place some of their principal Caciques in the power of the general. Rondeau fell into the snare, and took his measures so badly, that, before the exchange was made, his officers were suddenly made prisoners, and carried off at a gallop, enveloped by a cloud of Indians, who were soon out of sight. His cavalry was in no condition to follow the savages into the pampas, and he returned to the Tandil with the conviction that the Puelches tribes, as well as the Ranqueles, were combined in one and the same determination to have no more friendly intercourse with the Christians. After this affair nothing further was attempted, except to send out a party to explore the continuation of the range of the Tandil to the coast, of which the following was the result.