THE HEART OF THE ANTARCTIC 



the sea water below the ice and that of the air above it, 

 as soon as a contraction crack opened, the sea water 

 appeared to be steaming. A wall of thick vapour would 

 rise along the whole length of each crack. To this the 

 term of frost-smoke is sometimes applied. The water 

 vapour, as it rose, was being constantly condensed and 

 deposited on the walls of the narrow cracks, so that 

 gradually the interspace became filled with ice, and not 

 infrequently a ridge of soft ice would be built up along 

 the line of the old crack, to a height of 6 in. or so above 

 the general level of the surrounding ice. As the ice was 

 often traversed by a perfect network of these cracks, the 

 resulting ridges gave the ice-surface the appearance of 

 Indian paddy-fields, with their dividing " bunds," or mud 

 walls. 



The sea ice was usually separated from the shore-ice, 

 or ice-foot, by one or more well-marked tide-cracks. In 

 McMurdo Sound, near our winter quarters, the tidal 

 range of from 2 ft. to 3 ft. was quite sufficient to fracture 

 the ice in contact with the land. The seals took advantage 

 of these tide-cracks, and used them as blow-holes. 



The chief geological work done by the sea ice, as far 

 as we could ascertain, was the transport seawards of wind- 

 blown rock detritus lodged on the shore-ice and ice-foot, 

 in the manner about to be described. 



Ice-foot or Shore-ice. — On first arriving on the 

 shores of the Antarctic after the breaking up of sea ice, 

 towards the end of the sunmier, one is puzzled to account 

 for the low cliff, part snow, part ice, which almost every- 

 where fringes the coast and so makes landing from a boat 

 difficult. This fringe is seen to be made up partly of ice 

 at its base, resembling somewhat the stalagmites of lime- 

 stone caves, partly of layers of compressed snow, in 

 some cases alternating with bands of sand and gravel. 

 The ice-foot generally rises to a height of 6 to 10 ft* 



290 



