Condamine and Smyth, in descending the Amazon, mention the great depth and volume of water at the mouth of the Purus: Herndon heard from a Brazilian trader at Barra, who had ascended its stream for some distance, that it was of great size, and without obstructions; and Haënke, in the last century, arguing from reliable geographical data which he had collected from Indians, stated his conviction that a very large river, flowing from the Andes east of Cuzco, reached the Amazon to the westward of the mouth of the Madeira. This is the sum of our knowledge of the mouth and lower course of the Purus. The tributaries which flow into it drain the eastern slopes of the Andes, from the latitude of Cuzco quite to the frontier of Bolivia--that frontier dividing the streams flowing into the Purus, on the Peruvian side, from those which feed the Beni, on the Bolivian. These affluents of the Purus are divided into three distinct systems: the furthest to the north and west, consisting of the streams flowing through the great valley of Paucartambo, which unite under the name of the Madre de Dios, or Amaru-mayu; the middle system, draining the ravines of Marcapata and Ollachea; and the southern and eastern, being the numerous rivers in the province of Caravaya, as far as the Bolivian frontier, which unite as the Ynambari. The Madre de Dios and Ynambari together form the main stream of the Purus. The Paucartambo system is the only one which has, as yet, been described by modern explorers. In Spanish times the streams which compose it were explored, and farms of cacao and coca were established on their banks; and in the end of the last century an expedition was sent to explore the course of the Madre de Dios, under an officer named Don Tiburcio de Landa. This must have been at some time previous to 1780, for Landa was killed in that year in the great rebellion of the Indians under Tupac Amaru.[286] After the declaration of Peruvian independence, General Gamarra, the first Republican Prefect of Cuzco, sent an expedition to protect the farms in the valley of Paucartambo from the encroachments of the wild Chuncho Indians, and to explore the Madre de Dios. It was commanded by a Dr. Sevallos, now a very old man, retired to a farm in the Caravaya forests, but he has, unfortunately, lost his journal. General Miller made an expedition into the same region in 1835, and penetrated to a greater distance than any other explorer before or since. A very brief account of his journey was published in the 'Royal Geographical Society's Journal' for 1836; but there is a much fuller and most interesting journal kept by this gallant veteran, which has never been printed. In 1852 Lieut. Gibbon, U.S.N., entered the valleys of Paucartambo; and in 1853 I explored a part of the course of its principal stream, the Tono.[287] Another expedition to explore this region, under the sanction and with the aid of the Peruvian Government, was undertaken by some native