I902J ANTARCTIC DISADVANTAGES 309 



varied greatly, but, taking an average condition, I doubt 

 whether we should have approached twenty miles over it by 

 expending an equal amount of energy to that which gave us 

 the thirty-six miles over the sea-ice. This argues a great 

 difference, and it is one that cannot be wholly explained. 

 Of course the primary condition of importance on which 

 the excellence of a surface depends is its relative hardness. 

 The snow surface of the sea-ice, when we crossed it so 

 rapidly, was so hard that the sledges left but a faint track ; at 

 the same time, it was not too hard to prevent one's fur-clad 

 foot from getting some grip at each step. On the other hand, 

 the sledges always left a well-marked track in the barrier 

 surface, and at each step one sank ankle-deep and sometimes 

 even deeper. But this is by no means the only factor that 

 governs a surface ; wind, sun, temperature, and the age of the 

 snowfall are all elements that affect it, increasing or decreasing 

 the friction on the sledge-runners in a manner that is often 

 inexplicable and sometimes exasperating. All such changes, 

 however, will be dealt with in the accounts of our sledge 

 journeys ; for the present it is only necessary to point out that 

 it is difficult to define exactly what constitutes a good or a bad 

 sledging surface. 



Besides being dependent on the climatic conditions and 

 on the nature of the snow over which he journeys, the sledge- 

 traveller has to consider other obstructions which more 

 obviously hinder his progress. On the sea-ice he may meet 

 with those elevated fragments pressed up by the movement 

 and distortion of the ice-sheet, which are commonly called 

 hummocks ; on sea or on land he may encounter regions 

 where the wind has ploughed the snow into furrows, the waves 

 between which are technically termed sastrugi; on the land- 

 ice he may meet vast ridges and chasms, cracks and crevasses, 

 mild and gentle undulations, or any other resultant of the 

 irresistible movement of an ice-sheet. All such obstacles are 

 very obvious deterrents, and exist both in the North and in 

 the South, but to a different degree. Sea-ice in the South, 

 as far as we know it, is extraordinarily free from hummocks. 



