Mudo lamento de la vastissima, y numerosa Gentilidad, que habita las dilatadas margenes del caudaloso Orinoco, su origen, y vertientes, à los piadosos oídos de la Magestad Catholica de las Españas, nuestro señor Don Phelipe Quinto (que Dios guarde).

This extensive relation is of the utmost importance as it is the first detailled document about the Jesuit missions about the Orinoco River and its main tributaries. Father Tapia gives a very accurate description of the Indians tribes living in this region, dealing with their language and their customs. He also decribes the Indians’ paths in the forrest, the border demarcations between tribes, and the flora and fauna of the Orinoco.  The work also contains an account of the death of the Flemish Jesuit Ignacio Tohebast who was killed by the Indians.