24-JL ANNALS NEW YORK ACADEMY OF SCIENCES 



In the south of Pern, it is in part occupied by the most picturesque 

 inland body of water of which the South American continent can boast, 

 the well-known Lake Titicaca. To the southwest of Lake Titicaca, we 

 have a somewhat dissected area drained by the Eivers Blanco, Canco- 

 marca and Maure. To the southeast, we find the extension of the broad 

 plains leading to La Paz, Bolivia. To the northeast, the Titicaca plains 

 soon melt away in the foothills of the East Cordillera, whose long un- 

 broken front, as seen from Lake Titicaca, presents a spectacle of moun- 

 tain scenery that is not duplicated until we reach central Peru. To the 

 northwest, we find that the Titicaca plains give place quite rapidly to a 

 highly dissected belt. The streams coming to the Titicaca basin from the 

 northwest are short, and their floors are very much aggraded, representing 

 arm-like extensions of the enormous pampas to the north of the lake. As 

 soon as we pass over the drainage divide at La Raya, we drop into an 

 area that has been deeply cut by the drainage system of the Apurimac. 

 It represents the headwaters of the Tambo and Ilcayali, the latter join- 

 ing the Marafion, and it, in turn, emptying into the Amazon. Of this 

 stretch of country, the writer is personally acquainted with the Cuzco 

 section, or rather, the belt etxending from La Paz, Bolivia, to a cross 

 section through Cuzco. 



Let us search for a locality where Ave can get a clear sweeping view, 

 both to the northeast and southwest. To do this, we must ascend to the 

 upland surface into which the Urubamba and Apurimac systems of drain- 

 age have deeply incised themselves. Various points of vantage may be 

 found in the highlands overlooking the valley of the Urubamba be- 

 tween Cuzco and the Pueblo Urubamba, or from high points overlooking 

 the valley of the Apurimac. Selecting a high jDoint among the latter, and 

 looking to the northeast, we will see, in the foreground, as it were, really 

 two ranges looming up before us, and far above the level on which we are 

 standing, one lying between the Apurimac and the Urubamba, and the 

 other between the Urubamba and the head-waters of the Madre de Dios. 

 While topographically these form parts of the East Cordillera, I am 

 inclined to believe, from a geological point of view, that only the range 

 lying northeast of the Urubamba- Villcanota valleys belongs in the East 

 Cordillera proper. One could not wish for a more varied bit of mountain 

 scenery than that from Sicuani to Cuzco. To the northeast, we have the 

 pinnacle, spire and knob-like topography that characterizes a region of 

 great volcanic activity. To the southwest, however, we have a very dif- 

 ferent expression, that which characterizes a belt occupied largely by 

 sedimentary formations, here and there disturbed by local volcanic in- 

 trusions. 



