82 R. M. Deeley — Glaciers of the Yakutat Bay, Alaska. 



argument that ice is not a powerful agent of erosion, and that it acts 

 to protect rather than erode. This conclusion has been based largely 

 on observations along the margins of weak dwindling valley glaciers. 



" In the face of such evidence that ice has eroded, it is hardly 

 demanded that one shall show that it really can erode. Nevertheless 

 it may not be amiss to point out several facts bearing directly on the 

 question. In the first place there was an enormous thickness of ice, 

 supplied from many tributaries and without doubt flowing with 

 comparative rapidity through the valleys. Second there is the direct 

 evidence that ice was actually eroding. The roche moutonnee surfaces, 

 the evidence of plucking, the polished, scratched, grooved, and fluted 

 rock exposures in all parts of the inlet, and the extensive moraine 

 deposits, all testify to the fact of erosion by the glaciers, and the 

 existing glaciers add another evidence, namely, that of rock flour 

 issuing from the ice fronts in the glacial streams. 



"Whether one assumes that this erosion amounts to an inch in 

 a year or an inch in a score of years, the fact of ice erosion must be 

 accepted. One might see a small stream of clear water at the bottom 

 of a deep gorge and say, correctly, that such a stream can not have 

 formed so profound a gorge . . . But the flood stream, like the ice 

 flood, is a different agent in degree." 



It must be always remembered that all glaciated surfaces were last 

 sculptured by the thin end of the retreating glacier which finished by 

 polishing only. A finished statue frequently shows no signs of the 

 rough work done by the chisel to commence with. 



Between Russell Fiord and the Alsek River to the east the 

 mountains rise to a height of four or five thousand feet. "The 

 mountain slopes, where not too steep, are snow-covered, and all the 

 valleys are deeply filled with streams of ice." " Such a condition of 

 ice flood, drowning the valleys and rising high on the slopes of the 

 mountains, which project as nunataks above the glaciers, is so different 

 from that of the normal valley glacier that it seems to demand 

 a special name ; it is therefore proposed to apply to it the name 

 ' through glacier'." In such a region the ice-flow will not always be 

 from the divide. It will sometimes flow over a divide and cut a through 

 valley like Russell Fiord itself. 



Professor Tarr mentions an interesting case, which he saw, of 

 a hanging valley glacier, more than a mile in length, slide bodily out 

 of its valley ; for this reason the valley was named Fallen Glacier Gulch. 



It appears that the glaciers which enter the Russell Fiord are melted 

 most rapidly at the surface of the sea. Below the water a snout 

 of ice projects. Masses of this break off and rise to the surface. 

 "Bergs immediately in front of the glacier are prevailingly either 

 white, blue, or black in colour. The white bergs are derived from the 

 ice walls above the sea ; the blue ones, which are often a beautiful 

 Antwerp blue, rise from below the water ; the purely black icebergs, 

 which are by no means uncommon, rise mainly from the base of the 

 glacier, though a few fall from the debris-covered portions of the ice 

 front." " In the warm summer air the blue icebergs quickly whiten." 

 The sun breaks up the ice into its constituent granules, and the surface 

 whitens owing to refraction and reflection from the granules.. 



