The Birth of Bergs. 49 



beloAV water more rapidly than it does in the air, is shoAvn liv 

 the fact that icebergs roll over, which is due to this alone. It 

 is quite possible that the icebergs darkened by mud and rock 

 may not have come from the bottom, but may be merely expos- 

 ing the side of some old crevasse into which debris from a sur- 

 face moraine has fallen. The bergs which we saw rise from 

 below the water usually came up after a very heavy fall from 

 above, as though some crack had been Started by the shock of 

 the falling ice ; only a few of them were discolored by debris ; 

 most were pure blue ice * ^loreover, they did not rise very 

 high out of the water. All this makes me think that the}' did 

 not originate at any very great depth. Just as a stick thrown 

 obliquely into the water may rise again at an angle, so a berg, 

 on account of its shape, may rise so obliquely as only to reach 

 the surface some distance from the ice-front, thus suggesting 

 that the glacier sends out a foot along the bottom of the inlet, 

 from the end of which the ice breaks off; but the considerations 

 I have mentioned make it evident, I think, that this is not the 

 case. A series of observations on the temperature and density 

 of the water of Muir inlet at different depths and at different 

 distances from the ice would undoubtedlj'' afford information 

 that would enable us to reason very accurately about the form of 

 the ice-front below the water. 



The ice at the bottom of the glacier in contact with its bed 

 moves very slowlj^, and it is not improbable that the melting, 

 Avhere it meets the salt water, quite equals the advance. The 

 slope from that point up is determined l\v the strength of the 

 ice. If the progression of the bottom is greater than the rate of 

 melting, the glacier will advance until it comes to a broader part 

 of the tiord, and thus presents a broader front to the water. If 

 the fiord were of uniform depth and breadth, the ice could only 

 find a position of equilibrium at one end or the other. 



The efiect of the depth of the water in determining the posi- 

 tion of the glacier's end is not apparent. As the depth is greater 

 the pressure against the ice is greater, but at the same'^ime the 

 water produces a greater upward pressure on the ice, diminish- 

 ing its pressure against its bed and thus reducing the friction. 

 Although these effects cannot balance at all depths, I am unable 

 to indicate which one is in general the stronger. 



* The discolored bergs seen by Mr Russell in Disenchantment bay are 

 pro]ial)ly f'voni the debris-covered parts of the neigliboring glaciers. 



