OCEANOGRAPHY AND SEA-ICE 



Hence they are much more irregular and crevassed 

 than the southern tabular bergs. Still the southern 

 examples are often tilfed, owing to fragments breaking 

 off asymmetrically ; or they may be domed and derived 

 perhaps from the undulations of a small glacier tongue. 

 Many of the bergs are traversed by huge vertical cracks, 

 between which portions seem to have slipped down — 

 forming *'graben," in geological language. (These 

 cracks originated in the land-ice as already shown in 

 Figure 21.) On one occasion I saw a huge isolated 

 column rising one hundred feet into the air just like 

 the "Old Man of Hoy" and like that rock resulting 

 from wave erosion acting on vertical cracks. It was 

 attached to the adjacent tabular berg by the submerged 

 ''ram" of the iceberg, which is such a danger to ship- 

 ping. Often the cracks weather into caves. 



Many bergs are grounded near the Antarctic coast 

 and several of these were closely examined near Cape 

 Evans. The wonderful Tunnel Berg, of which the 

 photograph by Pouting has so often been reproduced 

 had a varied life history. When we first saw it in 

 January, 191 1, the berg projected about one hundred 

 feet above the sea-ice and was pierced by an oval tunnel 

 about fifty feet high and twenty feet across. I have 

 little doubt that this picturesque tunnel was a thaw- 

 water channel (cut out of the original glacier) of the 

 same type as wt saw on the Koettlitz Glacier. This 

 mass of ice broke away and floated so that the "bedding 

 planes" (as we may term them) wTre now nearly ver- 

 tical, as also was the tunnel. During the winter we 

 may assume that a large fragment broke off the south 



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