A CONTRIBUTION TO THE STUDY OF ICE-STRUCTURES 



17 



The reason for the high specific gravity of the first foot of the sea-ice has been men- 

 tioned. Below, as the crystallisation becomes slower, expulsion of the salt is increasingly 

 more effective. The fifth foot, which was in contact with the sea-water below, was 

 somewhat cellular and saturated with sea-water, which did not all drain out before 

 part became frozen in the specimen, hence the greater salinity. 



IV. ICE-STALACTITES 



Besides fresh-water icicles there were to be found along the ice-foot which formed 

 at Cape Royds grottos draped with stalactites of less simple structure. The ice of 

 the ice-foot is in all cases very briny, consisting largely of frozen sea-spray. On account 

 of the fact that the melting-point of brine is very much below that of pure ice, there is 



HoUow Core 



Cellular Layers 

 '5 



Fig. 5. Cross-Section of Stalactite 



a tendency for the former to ooze out of the ice-foot and drip back into the sea. As 

 the freezing of brine solution depends upon its concentration, the brine which drips 

 from the ice-foot at low temperatures is more concentrated than that at high tempera- 

 tures. In the autumn, with falling temperatures, the brine which oozes from the ice- 

 face becomes somewhat more chilled before it has time to drop, and so leaves behind at 

 that point a little pure ice. In time the dripping-point becomes more pronounced and 

 stalactites, sometimes several feet in length, are built up gradually. A stalactite from 

 the ice -foot at the Penguin Rookery was examined and found to be constructed of 

 alternating concentric rings of compact ice and of cellular ice. The centre was in the form 

 of a somewhat cellular hollow tube. The section figured here is a reproduction of the 

 cross-section traced from the stalactite itself (Fig. 5). 



On thawing a stalactite the commencement of freezing of the thaw-water was found 

 to be 29-5° F. 



A quantity of the drip from stalactites at the ice-foot was collected in the early 

 autumn and found to commence freezing at 8° F. At -5° F. it had assumed the form 

 of a paste — a mixture of unfrozen cryohydrate and fine ice-leaves. 



After the sea in the vicinity had become finally frozen over, snow drifting over 

 the floe banked up along the shores, obliterating much of the original ice-foot. Where 

 stalactite -draped caverns remained, the stalactites themselves were found to have 



