THE HEAET OF THE ANTARCTIC 



three miles to see if there was any way at all practicable 

 for the sledge out of these mazes of chasms, undula- 

 tions and seracs. Mackay and I were roped together 

 for this exploratory work, and fell into about a score of 

 crevasses before we returned to camp, though in this 

 case we never actually fell with our head and shoulders 

 below the lids of the crevasses, as they were mostly 

 filled at the surface with tough snow. We had left a 

 black signal flag on top of a conspicuous ice mound as 

 a guide to us as to the whereabouts of the camp, and 

 we found this a welcome beacon when we started to 

 return, as it was by no means an easy task finding one's 

 way across this storm-tossed ice sea, even when one was 

 only a mile or two from the camp. On our return we 

 found that Mawson was just completing his observations. 

 He found that the dip of the needle here was 2^° o& the 

 vertical. We brought the tent down from where he had 

 been taking magnetic observations, and treading warily, 

 because of crevasses, set it up again close to our sledge, 

 and had lunch. 



We noticed in the case of the snow lids over crevasses 

 that they were covered by a very pretty moss-hke 

 growth of pointed ice crystals. This growth was 

 apparently due to a slow upward steaming of moist 

 air from the spaces between the walls of the crevasses 

 below. Possibly during the day the air beneath the 

 snow lids may become slightly warmed, and as the 

 temperature falls at night, particularly under the 

 influence of the plateau wind, a slow percolation of the 

 warm air through the snow lid may take place, and the 

 small amount of moisture in it is deposited on the 

 surface of the Hd on coming in contact with the colder 

 air outside. This process, continued from day to day, 

 gradually builds up these moss-like crystals. 



That afternoon we discussed the situation at some 



136 



