There are two distinct hydrographic systems in Ecuador--the streams that flow south-eastward to the Marañon, or Amazon, and those which flow westward to the Pacific. The southern part of the great central plateau is arid and has a very light rainfall; it has no streams, therefore, except from melting snows, and the higher elevations which receive the impact of the easterly winds. Farther north the rainfall becomes heavier, the plateau is covered with vegetation, and a considerable number of small rivers flow westward through the Cordillera to the Pacific. The Eastern Cordillera, or Andes, forms the water-parting between the two systems. The largest of the eastward-flowing rivers is the Napo, which rises in the eastern defiles of Cotopaxi and Sincholagua--the principal source being the Rio del Valle, which traverses the Valle Vicioso. It at first flows south by east, and at the village of Napo is 1450 ft. above sea-level, at the mouth of the Coca 858 ft., at the mouth of the Aguarico 586 ft., 500 at the mouth of the Curaray, and 385 at its junction with the Marañon. Orton estimates its current at Napo in the month of November as 6 m. an hour; in the next 80 m. the river falls 350 ft. and produces a fine series of rapids; and from Santa Rosa downwards the rate is not less than 4 m. an hour. Its breadth at Napo is only 120 ft., but at Coca it has widened to 1500 ft., and at its mouth to nearly 1 m. Like most of the large Amazon tributaries, its discharge into the Marañon is through several distinct channels. The Napo is navigable for steam-boats for some distance above the mouth of the Coca, and thence for canoes as far as the Cando cataract, 3332 ft. above the sea. Its total length is 920 m. The principal tributaries of the Napo are the Coca and Aguarico from the north, and the Curaray from the south. The Coca rises on the eastern slopes of the Andes near Cayambe and the Guamani range, and flows eastward near the equator to San Rafael (about 76° 30' W. long.), where it turns sharply southward to a junction with the Napo in about lat. 1° S., long. 76° W. The Coca forms the provisional boundary line between Ecuador and Colombia from its source to the Napo. The Aguarico also rises on the eastern slopes of the Andes north of Cayambe and flows south-eastward to a junction with the Napo in about long. 75° W., its length being roughly estimated at 420 m. Little is known of its course, or of the country through which it flows, which is provisionally occupied by Colombia. The Curaray has its sources in the defiles of the Cerros de Llanganati, and flows south-eastward to the Napo, its length being estimated at 490 m. Its lower course is sluggish, where its waters are made unpalatable by a reddish slime. The Napo and its tributaries are celebrated in the early history of South America as the route by which Gonzalo Pizarro and Orellana first reached the Amazon, and it was