42 E. C. ANDREWS 



or mainly functional in readjusting the grade along which a mighty 

 flood only could do effective work. Until such time, aggradation 

 at the majority of points will ensue. Thus it is with our retreat- 

 ing ice-stream. The deeply scored channel, the huge rock 

 basins (between widely separated canyon precipices adorned with 

 ''hanging" valleys), marked the grade along which the ice during 

 a maximum ^ood only could accomphsh work. The least retreat 

 of the flood would cause cessation of cutting at these points. Although 

 the canyon ice-overflow might be stopped, yet the canyon itself 

 might be full. Nevertheless, cutting work would be ceased along 

 these points of maximum excavation, since pressure and speed have 

 been reduced in the central channels. The only work the glaciers 

 can now accomplish along the rock basins will be the partial, or at 

 times even complete, obliteration of the deep grooves which marked 

 their high-flood attack. Hence we should expect the rock basins to 

 lose their deep chisel marks, and slight scratches,' or even smooth 

 surfaces, to be substituted as the power of scouring became pro- 

 gressively feebler. Huge loads of rubbish could still be carried, and 

 these would be dumped just below the rock-basin mouths. With 

 stifl farther ice-retreat the loads would be dumped into the lower 

 ends of the rock basins (lakes and sounds). Hence would arise 

 great shallowing up at the sound entrances. With farther recession 

 the glaciers would be unable to even move their former bottom loads, 

 and then would ensue the overriding of moraines (formerly the tools 

 with which the glacier accomplished its work). Still later stages 

 would be marked by stagnant or inactive glaciers. Thus arise, in 

 the author's opinion, the inactive glaciers of Alaskan, Norwegian, 

 Alpine, and other canyon bases. They are enormous ice-masses, it 

 is true, but the fact must not be lost sight of that they are but the 

 veriest pigmies as compared with their colossal representatives during 

 the Ice Flood. Still again, the channel grades existent at present were 

 formed during the flood, and as such the channels of today at these 

 locahties are too wide, and possessed of slopes too much reduced, 

 for corrasion to be noticeable in the present ice-drought stage. 



I The declines of the troughs would be more scoured in these later stages than 

 the lower inclined floors. Nevertheless, in the Ice Period these were more deeply 

 chiseled. 



