160 GLACIOLOGY 



common nearer the surface at a depth of from 1 to 2 feet below the hexagonal 

 prismatic ice. 



The second and most common type was a clear ice with very few bubbles, the 

 latter of various sizes ; it forms by far the greatest amount of ice present in this 

 portion of the lake, and is frequently traversed by the fracture planes mentioned 

 above. 



A third type, occasionally met with, had bubbles of similar size and frequency to 

 the last, but with the bubbles drawn out into tubes, although the direction from 



ar 



ITTTTTITTTI 



- Columnar Ice 





Ice with Fragments of Alga 



icB-cemenied Breccia witti 

 Fragments covered with Fungus 



Fig. 52. Section Blue Lake Trench 



which they had elongated was sufficiently indicated by a bulging of the tube at the 

 bottom, so that the bubble and tube bore a strong resemblance to a thermometer. 



The last type observed was only in local patches about 6 inches square. In it 

 the bubbles appear very similar to those of the last type, but are much smaller and 

 more numerous, giving quite a lined structure to the ice. This type frequently 

 appeared quite suddenly above perfectly clear ice. On examination Mawson found 

 these elongated bubbles to be hexagonal in shape like negative ice crystals. In one 

 or two cases these drawn-out bubbles ended abruptly against one of the fracture 

 planes already noted. 



