Ayusbamba (Peru) Fossil Beds. 



131 



be added morainal accumulations and the ungraded character 

 of the upper stream courses, which are in marked contrast with 

 their lower reaches. So far as observed, direct abrasion by 

 glaciers was not effective below 12,500 or at most 12,300 feet. 

 The mountain heights above the lower limit of ice action pre- 



Fig. 5. 



Fig. 5. View from the Pass at the southern edge of the Ayusbamba fossil 

 beds, looking south into the Apurimac canyon. Note the rock and alluvial 

 terraces. 



sent both rounded bosses and sharp aretes, — features character- 

 istic of glaciated surfaces. Summits below 12,300 feet assume 

 forms consistent with the role which they play as part of a sub- 

 maturely developed landscape. Along the highland trails 

 north from Ayusbamba and also east toward Paruro irregu- 

 larly distributed erratics, incipient cirques, bowlder trains, and 



