74 GLACIOLOGY 



northwards, and due to marine erosion effected, when the sea is free of ice, by 

 the fierce bHzzard winds. 



Fig. 30 shows, amongst other things, the numerous and large sastrugi raised 

 thex'e by the southerly blizzards. 



The blizzard first breaks up the sea ice, then piles it as drift pack against the 

 southern side of the Tongue. The jagged tilted slabs of this pack ice shelter the 

 drifting snow, and give origin to sastrugi of exceptional size. It is obvious that the 

 drift snow which has helped to round off the weather side of this Tongue is carried 

 in enormous quantities across it, forming immense drifts to leeward, that is, on 

 its northern side. It may be suggested that these drifts, forming at first on sea 

 ice, if the sea ice does not break away the same year, may eventually pass into a 

 sjDecies of barrier formation, partly ice, partly old snow. 



That this Tongue is afloat is, we think, proved by the entii'e absence of any 

 trace of tide-crack at its southern side. Along its northern side the sea ice was 

 slightly cracked, but probably this was merely due to small differential movements 

 between the sea ice and the Tongue, as, even if they both rise and fall together with 

 the tides, the inertia of the latter is so much greater than that of the sea ice, that 

 some cracking of the sea ice at its junction with the Tongue may be reasonably 

 expected. 



We conclude, therefore, provisionally that this ice is afloat. A glance at the 

 plan and the sketches shows that it is not only the blizzard wind which drifts snow 

 over the Tongue, but the plateau wind also. The latter wind blows from off the 

 plateau coastwards down the depression of the Mawson Glacier, and tends to build 

 the Nordenskjold out in an easterly direction. This plateau wind blows fi-om a 

 direction about W. 10° N. 



The following plan and cross section indicate the probable structure of the 

 Tongue (Fig. 31). 



The surface of the Nordenskjold Ice Tongue is on the whole very flat and even, 

 in striking contrast in this respect to the Drygalski. 



In the area between the rounded hummocks of greenish ice forming its southern 

 margin and the consolidated layers of old snow forming its northern edge the surface 

 is formed entirely of hard snow covered with a thin glaze, due to thawing and re- 

 freezing of the snow. Its surface shows broad, but very gentle, undulations, with 

 intervals of about a quarter of a mile between the summit of one undulation and 

 that of the next. 



Here and there, especially near its southern margin, hummocky sastrugi project 

 5 or 6 feet above its general surface. Towards the centre of the Tongue the sasti'ugi 

 are comparatively insignificant, only a few inches in height. Certainly the plateau 

 wind in this neighbourhood is quite subordinate in force to the southerly blizzards, 

 as far as one can judge from the sastrugi. This is the reverse of what is the case 

 near the Drygalski. The jalateau wind would, therefore, scarcely be strong enough to 



