GLACIAL FEATURES 303 



we find there under the conditions of snow motion outlined in 

 earlier paragraphs. It is also noteworthy that it is at such a 

 point of concentrated discharge that crevasses no sooner open than 

 they are closed by the advancing snow masses. To my mind the 

 whole action is eminently representative of the action taking 

 place elsewhere along the cirque wall on a smaller scale. 



What seems a good test of the explanation of cirques here 

 proposed was made in those localities in the Maritime Cordillera, 

 where large snowbanks but not glaciers affect the form of the 

 catchment basins. A typical case is shown in Fig. 201. As in 

 many other cases we have here a great lava plateau broken fre- 

 quently by volcanic cones of variable composition. Some are of 

 lava, others consist of ashes, still others of tuff and lava and 

 ashes. At lower elevations on the east, as at 16,000 feet between 

 Antabamba and Huancarama, evidences of long and powerful 

 glaciers are both numerous and convincing. But as we rise still 

 higher the glaciated topography is buried progressively deeper 

 under the varying products of volcanic action, until finally at the 

 summit of the lava fields all evidences of glaciation disappear in 

 the greater part of the country between Huancarama and the 

 main divide. Nevertheless, the summit forms are in many cases 

 as significantly altered as if they had been molded by ice. Pre- 

 cipitous cirque walls surround a snow-filled amphitheater, and 

 the process of deepening goes forward under one's eyes. No 

 moraines block the basin outlets, no U-shaped valleys lead for- 

 ward from them. We have here to do with post-glacial action 

 pure and simple, the volcanoes having been formed since the close 

 of the Pleistocene. 



Likewise in the pass on the main divide, the perpetual snow 

 has begun the recessing of the very recent volcanoes bordering 

 the pass. The products of snow action, muds and sands up to very 

 coarse gravel, glaciated in texture with an intermingling of 

 blocks up to six inches in diameter in the steeper places, are col- 

 lected into considerable masses at the snowline, where they form 

 broad sheets of waste so boggy as to be impassable except by care- 

 fully selected routes. No ice action whatever is visible below 



