PERU. In Peru, Bolivia, and the northern part of Chile, the system is much broader and more complex. The Andes of Peru consist of three ranges, the two westernmost being the Maritime or Black, and the Central Cordillera, trending parallel to one another and to the coast, and in the north separated only by a narrow, high plateau, known as the Puna, with an aver age height of 12,500 feet, and in the south by the narrow valley of the Rio Huay. The East ern Cordillera, though otherwise continuous, is cut through by no less than six of the head tribu taries of the Amazon. The broad, elevated region lying between this and the Cordillera Central, known as the Sierra, is broken by mountain spurs, with broad valleys and plateaus. East of the Eastern Cordillera, or the Andes, as it is locally known, are several lower ranges, trend ing_ parallel with the system, and separating tributaries of the Amazon. The Maritime and Central Cordillera are composed of crystalline and volcanic rocks, with stratified beds of .Juras sic age resting upon their outer flanks. The Eastern Cordillera is composed mainly of strati fied beds of Silurian age, with some intrusions of granite. These ranges are connected at the
mountain knot of Cerro de Pasco, 14,293 feet high, and again further to the southeast, at the Knot of Vilcanota, 17,390 feet. South of this latter peak the Central and Eastern Cordillera enclose the lofty plateau on which is Lake Titi caca, situated partly in Peru and partly in Bolivia, and 12,545 feet above the sea. North of the Cerro de Pasco, the Sierra comprises the upper valley of the Maranon, the largest and longest of the head branches of the Amazon, which cuts through the Eastern Cordillera just south of the Ecuador frontier. Between the Cerro de Pasco and the Knot of Vileanota, the Sierra is drained by the head streams of the Ucayali, a large tributary to the Amazon. These streams also cut gorges through the eastern range. This region was the site of the ancient Inca civilization, and is still thickly settled. Among the high peaks of this part of the Andes are Ilitascan, 22,051 feet; Huandoy, 21,089 feet ; Misti, 20,013; Chaeani, 19,820 feet; and Tutu paca, 18,960 feet.