EASTERN ANDES: CORDILLERA VILCAPAMPA 213 



extensively trimmed that the valley was turned into a trough. 

 The floor was smoothed and deepened and all the tributary gla- 

 ciers were either left high up on the bordering slopes or entered 

 the main valley with very steep profiles ; their lateral and terminal 

 moraines now hang in festoons on the steep side walls. Moreover, 

 the range crest is trimmed from the west so that the serrate sky- 

 line is a feature rarely seen from eastern viewpoints. This may 

 not hold true for more than a small part of the Cordillera. It was 

 probably emphasized here less by the contrasts already' noted 

 than by the geologic structure. The eastward-flowing glaciers 

 descended over dip slopes on highly inclined sandstones, as at 

 Pampaconas. Those flowing westward worked either in a jointed 

 granite or on the outcropping edges of the sandstones, where the 

 quarrying process known as glacial plucking permitted the devel- 

 opment of excessively steep slopes. 



There are few glacial steps in the eastern valleys. The west- 

 tern valleys have a marvelous display of this striking glacial fea- 

 ture. The accompanying hachure maps show them so well that 

 little description is needed. They are from 50 to 200 feet high. 

 Each one has a lake at its foot into which the divided stream 

 trickles over charming waterfalls. All of them are clearly asso- 

 ciated with a change in the volume of the glacier that carved the 

 valley. "Wherever a tributary glacier entered, or the side slopes 

 increased notably in area, a step was formed. By retreat some 

 of them became divided, for the process once begun would push 

 the step far up valley after the manner of an extinguishing water- 

 fall. 



The retreat of the steps, the abrasion of the rock, and the sap- 

 ping of the cirques at the valley heads excavated the upper val- 

 leys so deeply that they are nearly all, as W. D. Johnson has put 

 it, "down at the heel." Thus, above Anna, one plunges suddenly 

 from the smooth, grassy glades of the strongly glaciated valley 

 head down ovef the outer slopes of the lowermost terminal 

 moraine to the steep lower valley. Above the moraine are fine 

 pastures, in the steep valley below are thickets and rocky defiles. 

 There are long quiet reaches in the streams of the glaciated valley 



