66 THE ICE AGE IN NORTH AMERICA. 



were visible anywhere in that direction, it is presumable that 

 they had been recently excavated from preglacial forests simi- 

 lar in situation to that now exposed on the west below the 

 ice-front. 



The capacity of the ice to move, without disturbing them, 

 over such gravel deposits as covered the forests, is seen also 

 in the present condition of the southwestern corner of the 

 glacier itself. As the ice-front has retreated along that 

 shore, large masses of ice are still to be seen lapping over 

 upon the gravel. These are portions of the glacier still sus- 

 tained in place by the underlying gravel, while the water of 

 the inlet has carried the ice from the perpendicular bank 

 clear away. This phenomenon, and that of the general per- 

 pendicular front presented by the ice at the water's edge, 

 accord with the well-known fact that the surface of the ice 

 moves faster than the lower portions. Otherwise the ice- 

 columns at the front would not fall over into the water as 

 they do. 



The formation of kames, and of the knobs and kettle- 

 holes characteristic both of kames and of terminal moraines, 

 is illustrated in various places about the mouth of Muir Gla- 

 cier, but especially near the southwest corner, just above the 

 shoulder of the mountain where the last lateral branch comes 

 in from the west. This branch is retreating, and has already 

 begun to separate from the main glacier at its lower side, 

 where the subglacial stream passing the buried forest emerges. 

 Here a vast amount of water- worn debris covers the ice. ex- 

 tending up the glacier in the line of motion for a long dis- 

 tance. It is evident from the situation that, when the ice- 

 stream was a little fuller than now, and the subglacial stream 

 emerged considerably farther down, a great mass of debris 

 was spread out on the ice at an elevation considerably above 

 the bottom. Now that the front is retreating, this subglacial 

 stream occupies a long tunnel, twenty-hve or thirty feet high, 

 in a stratum of ice that is overlaid to a depth, in some places, 

 of fifteen or twenty feet with water-worn glacial debris. In 

 numerous places the roof of this tunnel has broken in, and 



