276 Sierra Club Bulletin. 



and, as in specific instances the distribution of tributary 

 streams suggested, to sink it again wherever the entrance 

 of a tributary tended to deepen it locally. At least it was 

 apparent that forward grade of bed is not essential to 

 glacier motion. 



Mt. Lyell in plan was a four-rayed star of thin aretes. 

 A small glacier occupied the cirque-basin, or amphi- 

 theater, facing northward ; and three other amphitheaters,, 

 empty of ice, opened severally east and west and south. 

 There was no vestige of an upland surface. It was 

 hardly to be doubted, however, that a stage of plateau 

 wasting had recently been closed here also, and the stage 

 of sinking initiated. Elsewhere combs and spires asso- 

 ciated with the tables, though invariably falling short of 

 their high levels, were recognizable as evanescent final 

 forms in the transition from a stream-modeled upland, 

 mantled with residual gravel, to a relative lowland of 

 glacial truncation displaying only sound, bare rock. The 

 old surface had not been worn down; it had been cut 

 away. Sapping and rude planation had been the process 

 — in the summit area, back from the channel-trough 

 heads. On that hypothesis the anomalous topography 

 of wide floors and upright forms in great variety at 

 once became interpretable. Its unit in plan was the 

 geometrical figure of the cirque. And the glacier makes 

 the cirque. 



Among the schrunds of various systems sharply lining 

 the Lyell glacier the great arc of the open "bergschrund," 

 a little out upon the ice, closely paralleled the arc of the 

 wall. It seemed possible that the bergschrund penetrated 

 to the wall-foot, along the line of its floor, and that sap- 

 ping there resulted from some special action to which this 



