THE HEART OF THE ANTARCTIC 



mites are produced only at very low temperatures, when 

 they may consist entirely of cryo-hydrate. 



Additional Notes by JAMES MURRAY 



Sea-ice. — ^When a crack opened out to a yard or 

 more in width it was very quickly filled with new ice. 

 The prisms composing this grew out horizontally from 

 the older ice at each side. They were straight and at right 

 angles to the edges of the crack, except where that was 

 abruptly bent or curved, when the adjustment to the in- 

 fluence of the two sides of the angle produced oblique or 

 even curved prisms. Good photographs of this horizontal 

 prismatic ice were obtained. 



Polygonal plates of thin ice accumulated round the 

 dredging hne when left undisturbed in the sea for some 

 time, as previously noticed by Hodgson. At Cape Royds 

 this only occurred late in the season, and seemed to be 

 much less in amount than at Hut Point, probably on 

 account of the higher temperatures which we experienced. 



Prismatic Ice. — It has been explained (by Mawson) 

 how the vertical prismatic structure of the irregular sur- 

 faces of hardened snow found on the lakes has originated 

 in the building up of additions to the prisms of lake ice. 

 Further light on the formation of prismatic ice was 

 afforded by observations in summer when he was absent. 



The fresh-water ice found under tranquil conditions 

 was clear and transparent, and the prismatic structure was 

 not evident. In colder weather it became revealed as a 

 very fine hexagonal reticulation. On the surface of hard- 

 ened snow-drifts prismatic structure was developed while 

 the lower layers of the drift remained as snow, and there- 

 fore independently of the lake ice prisms as a foundation. 



The most interesting formation of prismatic structure 



360 



