of the Cuzco Valley, Peru. 



33 



the sandstone of Catunga-Machu and the limestone of the Yuca 

 Parnpa. Consequent streams draining into the Oropesa and 

 Lucre basins also have small subsequent tributaries. ISTumer- 

 ous small obsequents carry water during the rainy season from 

 the slopes of minor cuestas. 



Streams in the Cuzco Valley have taken advantage of the 



Fig. 23. 



Fig. 23. Valley of the east branch of Rio Kkaira. 



major zones of faulting. For at least 3 miles of its course 

 the Huancaro follows a fault line, a fact that partly explains 

 its wide valley floor and its stage of development, which is 

 somewhat more mature than that of other transverse valleys 

 tributary to the Cuzco Basin. The Zappi portion of the 

 Huatanay likewise is located along a zone of faulting. Joint- 

 ing, commonly associated with minor faults, is well developed 

 in all the rocks about Cuzco. Many joints are open or filled 



Am. Joxtr. Sci.— Fourth Series, Vol. XLI, No. 241. — January, 1916. 

 3 



