42 



H. E. Gregory — A Geologic Reconnaissance 



imitation of glacial striation is seen on the Rodadero, at an 

 elevation of 11,750 feet (fig. 26). The grooves and stria? and 

 polished surfaces on this intrusive mass of augite diorite are 

 in fact so closely similar to features produced by ice that it 

 occasions no surprise to find them generally used as proof of 

 glaciation. When, however, the Rodadero is studied in detail, 

 the "glacial markings" are found to have been developed by 

 faulting. 19 



Fig. 26. 



Fig. 26. El Rodadero, near Cuzco. Hiram Bingham, photo. 



The twin peaks of Cerro Picol are bordered by cirques whose 

 characteristic features are well expressed. Below the pyra- 

 midal summits grass-cloaked or bare, striated rock platforms 

 bordered by precipitous inner walls testify to vigorous glacial 

 plucking. On the lip of a cirque facing Ccorao an unbroken 

 moraine rises to a height of 400 feet, inclosing a basin of 

 about 30 acres. The time elapsing since the retreat of the 

 ice from Picol has not been sufficient for the development of 

 surface drainage within the cirque, and water collected on its 

 swampy floor escapes by seepage to find its way to the Uru- 

 bamba. As viewed from Cuzco, 1 miles distant, this walled 



"Gregory: The Pvodadero; A Fault Plane of Unusual Aspect, this 

 Journal, xxxvii, pp. 289-298, 1914. 



