no 



MARIO ISr EXPEDITION TO DAVIS STRAIT AND BAFFIN BAY 



rience flowing outward tliroiigh the foreland. The blue-green 

 veins often give a very illusive effect as if the iceberg were cleft 

 from top to water line, and, instead of ice, one were looking directly 

 through the gap at the sky beyond. Another feature of interest is 

 The rock and earth debris which has become imbedded in the mass. 

 In this manner, doubtless, melting bergs drop considerable detritus 

 along their paths of drift. The earth usually lies in streaks and 

 veins striped across the sides and occasionalh^ stones and bowlders 

 the size of a man's body are seen imbedded in the top. 



The ununiform distribution of air and the banding of the ice 

 through melting and freezing are all processes Avhich tend to vary the 

 density from place to place in an ice sheet. Take one example: The 

 bottom layers of a glacier being under greater pressure than the upjier- 

 most few meters, results in the former beinrj much denser than the 



Earth Veins in a Greenland Iceberg 



Figure 72. — Many of the bergs drifting out of Davis Strait arc marlied witli one or 

 more veins of soil and debris wliicli were talieu up from the underlying bed when 

 the ice was a part of the glacier in Greenland. Icebergs may thus transport such 

 debris from the Arctic to the tropical regions of the Gulf Str(>am. (Photograph 

 by Lieut. Commander N. G. Ricketts. ) 



latter. Ahlmann, the Scandinavian glaciologist. I am informed, has 

 made several determinations regarding the density of glacial ice in 

 the Norwegian mountains, from the upper surface of a glacier down 

 to depths of several meters, and has found values which vary within 

 wide limits. The density of the interior of a glacier, according to 

 Ahlmann, differs little from the density of ice formed by fresh water 

 freezing in the ordinary manner (0.9167), but surface samples of 

 glaciers may be so porous as to give density values as low as 0.6. 

 The density of an iceberg being no more or less than a detached por- 

 tion of a glacier depends, therefore, on that part of the glacier from 

 which it calved. A berg composed mostly of the lower layers of an 

 ice sheet will be denser than one which broke away from the upper 

 surfaces of the same sheet. On the other hand, a given berg in 

 calving may embrace the entire glacier front, top to bottom, and in 



