214 THE ANDES OF SOUTHERN PERU 



heads besides pretty lakes and marshes. Below, the stream is 

 swift, almost torrential. Arma itself is built upon alluvial de- 

 posits of glacial origin. A mile farther down the valley is con- 

 stricted and steep-walled — really a canyon. 



Though the glaciers have retreated to the summit region, they 

 are by no means nearing extinction. The clear blue ice of the 

 glacier descending from Mt. Soiroccocha in the Arma Valley 

 seems almost to hang over the precipitous valley border. In 

 curious contrast to its suggestion of cold and storm is the patch 

 of dark green woodland which extends right up to its border. An 

 earthquake might easily cause the glacier to invade the woodland. 

 Some of the glaciers between Choquetira and Arma rest on 

 terminal moraines whose distal faces are from 200 to 300 feet 

 high. The ice descending southeasterly from Panta Mt. is a good 

 illustration. Earlier positions of the ice front are marked by 

 equally large moraines. The one nearest that engaged by the liv- 

 ing glacier confines a large lake that discharges through a gap in 

 the moraine and over a waterfall to the marshy floor of the valley. 



Eetreat has gone so far, however, that there are only a few 

 large glacier systems. Most of the tributaries have withdrawn 

 toward their snowfields. In place of the twenty distinct glaciers 

 now lying between the pass and the terminal moraine below Cho- 

 quetira, there was in glacial times one great glacier with twenty 

 minor tributaries. The cirques now partly filled with damp snow 

 must then have been overflowing with dry snow above and ice be- 

 low. Some of the glaciers were over a thousand feet thick ; a few 

 were, nearly two thousand feet thick, and the cirques that fed 

 them held snow and ice at least a half mile deep. Such a remark- 

 ably complete set of glacial features only 700 miles from the 

 equator is striking evidence of the moist climate on the windward 

 eastern part of the great Andean Cordillera, of the universal 

 change in climate in the glacial period, and of the powerful domi- 

 nating effects of ice erosion in this region of unsurpassed Alpine 

 relief. 



