50 THE ICE AGE IN NORTH AMERICA. 



streams of ice from the east and southwest have already 

 spent the most of their force on reaching the head of the 

 inlet ; and, were it not for this central ice-stream, a natural 

 equilibrium of forces would be established here independent 

 of the water, and no icebergs would be formed. The sur- 

 face of this central current of motion is extremely rough, so 

 that it is entirely out of the question to walk far out upon 

 it. On approaching this portion of the glacier from the 

 east the transverse crevasses diagonal to the line of motion 

 increase in number and size until the whole surface is broken 

 up into vast parallelograms, prisms, and tGwers of ice, sep- 

 arated by yawning and impassable chasms scores and hun- 

 dreds of feet in depth. Over this part of the ice the mo- 

 raines are interrupted and drawn out into thinner lines, often 

 appearing merely as patches of debris on separate masses of 

 ice. This portion of the ice-current presents a lighter 

 colored appearance than other portions, and the roughened 

 lines of motion can be followed, as far as the eye can reach, 

 through distant openings in the mountains to the north and 

 the northwest. 



The comparative rapidity of the motion in this part of 

 the ice is also manifest where it breaks off into the water at 

 the head of the inlet. As already said, the perpendicular 

 front of ice at the water's edge is from 250 to 300 feet in 

 height. From this front there is a constant succession of 

 falls of ice into the water, accompanied by loud reports. 

 Scarcely ten minutes, either day or night, passed during the 

 whole month without our being startled by such reports, and 

 frequently they were like thunder-claps or the booming of 

 cannon at the bombardment of a besieged city, and this, 

 though our camp was two and a half miles below the ice- 

 front. Sometimes this sound accompanied the actual fall of 

 masses of ice from the front, while at other times it was 

 merely from the formation of new crevasses or the enlarge- 

 ment of old ones. Repeatedly I have seen vast columns of 

 ice, extending up to the full height of the front, topple over 

 and fall into the water. How far these columns extended 



