Having now established throughout the extensive district, to which it is desired to direct the inquiring zeal of travellers, a dividing line bounding the basin of the Rio Branco, it still remains to remark, that for a century past no advance has taken place in our geographical knowledge of the country west of this valley between 61-1/2° and 65-1/2° W. longitude. The attempts repeatedly made by the Government of Spanish Guiana, since the expeditions of Iturria and Solano, to reach and to pass the Pacaraima mountains, have only produced very inconsiderable results. When the Spaniards, in travelling to the missions of the Catalonian Capuchin monks of Barceloneta at the confluence of the Caroni and the Rio Paragua, ascended the latter river, in going southward, to its junction with the Paraguamusi, they founded at the site of the latter junction the mission of Guirion, which at first received the pompous name of Ciudad de Guirion. I place it in about 4-1/2° of North latitude. From thence the governor Centurion, stimulated by the exaggerated accounts given by two Indian chiefs, Paranacare and Arimuicapi, of the powerful nation of the Ipurucotos, to search for el Dorado, prosecuted what were then called spiritual conquests still farther, and founded beyond the Pacaraima mountains the two villages of Santa Rosa and San Bautista de Caudacacla; the former on the higher eastern bank of the Uraricapara, a tributary of the Uraricuera which in the narrative of Rodriguez I find called Rio Curaricara; and the latter six or seven German (24 or 28 English) geographical miles farther to the east south-east. The astronomer of the Portuguese Boundary Commission, Don Antonio Pires de Sylva Pontes Leme, captain of a frigate, and the captain of engineers, Don Ricardo Franco d’Almeida de Serra, who between 1787 and 1804 surveyed with the greatest care the whole course of the Rio Branco and its upper branches, call the westernmost part of the Uraricapara “the Valley of Inundation.” They place the Spanish mission of Santa Rosa in 3°.46′ N. lat., and point out the route which leads from thence northward across the chain of mountains to the Caño Anocapra, an affluent of the Paraguamusi, by means of which one passes from the basin of the Rio Branco to that of the Caroni. Two maps of these Portuguese officers, which contain the whole details of the trigonometrical survey of the windings of the Rio Branco, the Uraricuera, the Tacutu, and the Mahu, have been kindly communicated to Colonel Lapie and myself by the Count of Linhares. These valuable unpublished documents, of which I have made use, are in the hands of the learned geographer who began a considerable time ago to have them engraved at his own expense. The Portuguese sometimes give the name of Rio Parime to the whole of the Rio Branco, and sometimes confine that denomination to one branch or tributary, the Uraricuera, below the Caño Mayari and above the old mission of San Antonio. As the