EASTERN ANDES: CORDILLERA VILCAPAMPA 209 



glaciers retreat and at last disappear. There would be evidences 

 of glaciation all about the ruins of the former loftier mountain, 

 but there would be no living glaciers. And yet the climate might 

 remain the same throughout. 



It is this "topographic" hypothesis that Keiss and Stiibel 

 accept for the Ecuadorean volcanoes. Moreover, the volcanoes of 

 Ecuador are practically on the equator — a very critical situation 

 when we wish to use the facts they exhibit in the solution of such 

 large problems as the contemporaneous glaciation of the two 

 hemispheres, or the periodic advance and retreat of the ice over 

 the whole earth. This is not the place to scrutinize either their 

 facts or their hypothesis, but I am under obligations to state very 

 emphatically that the glacial features of the Cordillera Vilca- 

 pampa require the climatic and not the topographic hypothesis. 

 Let us see why. 



The differences in degree of dissection and the flattening 

 gradient up-valley that we noted in a preceding paragraph leave 

 no doubt that each moraine of the bordering valleys in the Vilca- 

 pampa region, represents a prolonged period of stability in the 

 conditions of topography as well as of temperature and precipita- 

 tion. If change in topographic conditions is invoked to explain 

 retreat from one position to the other there is left no explanation 

 of the periodicity of retreat which has just been established. If 

 a period of cold is inaugurated and glaciers advance to an ulti- 

 mate position, they can retreat only through change of climate 

 effected either by general causes or by topographic development 

 to the point where the snowfields become restricted in size. In 

 the case of climatic change the ice changes are periodic. In the 

 case of retreat due to topographic change there should be a steady 

 or non-periodic falling back of the ice front as the catchment 

 basins decrease in elevation and the snow-gathering ridges tribu- 

 tary to them are reduced in height. 



Further, the matterhorns of the Cordillera Vilcapampa are not 

 bare but snow-covered, vigorous glaciers several miles in length 

 and large snowfields still survive and the divides are not aretes 

 but broad ridges. In addition, the last two moraines, composed 



