The canyons of the Amazon River system in the eastern ranges of the Andes of Peru are there known by the Indian name of pongo. The most famous of these is the Pongo de Manseriche, cut by the Marañon River through the eastern range of the Andes, where it emerges from the cordillera into the flat terrane of the Amazon Basin.
The Pongo de Manseriche lies nearly 500 miles upstream from Iquitos, and consequently nearly 3,000 miles above the mouth of the Amazon River. It is situated in the heart of the montaña, in a vast region the ownership of which has long been in dispute between Peru and Ecuador, but over which neither country exercises any police or other governmental control. The region is uninhabited except for small bands of seminomadic Aguaruna Indians. They are a branch of the savage Jivaro Indians, known principally through their gruesome custom . . .