314: Bowman — Geologic Relations of the Ouzco Remains. 



developed upon pre-Tertiary rock. Tertiary strata underlie 

 the benchland of the middle distance and appear as alternating 

 light and dark bands in fig. 13. Upon the Tertiary shales, 

 clays, and sandstones are the glacial gravels and sands. They 

 consist of a finer, older series, overlaid by a coarser, younger 

 series ; and both are now in process of dissection. Not only 



Fig. 10. 



Fig. 10. Distant snow-capped mountains, part of Cuzco Valley in middle 

 distance, and two series of glacial deposits, with unconformable relations, in 

 the foreground. 



the differences of composition, but also the line of separation 

 between the two series of gravels may be clearly seen in fig. 10. 

 The glacial gravels of the Cuzco basin occur on all of the 

 lower and most of the higher valley slopes and floors. They 

 lie upon older eroded rock and are themselves being eroded at 

 a rapid rate to-day no matter what their position. It follows 

 that they represent a period in which erosion was halted upon 

 all those slopes and on the floors of all those valleys on which 



