10 A CONTRIBUTION TO THE STUDY OF ICE-STRUCTURES 



preceding. The saline constituents were found to be sulphates and chlorides of sodium, 

 magnesium, calcium, and a small proportion of potassium. The freezing-point of the 

 water obtained by thawing a sample from the bottom was 27-5° F. The bulk of the ice 

 showed horizontal stratification strongly outlined by layers of gas-bubbles, each separated 

 by an average thickness of two inches of clear ice. The bubbles were as much as one- 

 third of an inch in diameter, and were generally elongated upwards in a short stem. This 

 clear stratified ice passes upwards through neve into irregular snow-banks. Below it 

 becomes less transparent and whiter. The last two inches in proximity to the bottom 

 were highly saline, resembling white enamel at a temperature of —30° F. — evidently 

 solidified cryohydrates. 



The transparent stratified ice of the upper portion of this ice-slab was crystallised in 

 vertical prisms, continuous from one layer to another. Downwards, the dimensions of 

 the prisms dwindled pari passu with the increasing salinity ; at the same time they 

 assumed a leaf-like form, arranged vertically and developed in optically continuous 

 bundles. Between the " ice-leaves " was frozen brine, easily distinguished by its white, 

 opaque appearance. This brine was evidently mechanically entrapped during the 

 development of the leaves. The bundles of " ice-leaves," though always in vertical 

 planes (actually normal to the cooling surface) were set at varying azimuths, and by 

 intergrowing produced a striking honeycomb structure in which the cells were occupied 

 by liquid or frozen cryohydric mixtures. This structure was well exemplified in 

 the bottom two inches, where the brine was highly concentrated. The " ice-leaves " 

 were brought out in relief by slowly warming a specimen until the cryohydric tempera- 

 ture was reached, when most of the brine drained away. A further critical examina- 

 tion of a sample from the bottom of the slab showed that in the freezing, as the 

 mother-liquor becomes more concentrated, the leaves of pure ice forming the cell 

 walls diminish in thickness with corresponding increase in contained salts. Finally, 

 where the crystallisation was from a pure cryohydrate, the honeycomb type, exhibit- 

 ing intersertal structure, sometimes was seen to merge into an even granular texture. 

 Sections both along the "ice-leaves" and across optically continuous bundles show 

 more or less distinctly the structure known in petrology as poikilitic. 



5. BLUE LAKE 



For details refer to Vol. I, p. 157. Blue Lake is an extensive fresh-water ice-lake. 

 Our experience and the evidence adduced show that the ice in this basin never more 

 than partially melts during a normal summer. A local thaw at the narrows was noted 

 in midsummer, but the structures exhibited by the ice made it clear that complete 

 thawing takes place only once in a long period of years. This is particularly interesting 

 on account of the fact that Murray found microscopic life amongst the remains of algae 

 frozen at the bottom, and the minute organisms on being thawed at the Hut again 

 sprang into life. 



Qualitative chemical tests showed the ice to be exceptionally pure. Only the faintest 

 trace of chloride could be detected in that between the surface and four feet. At greater 

 depths it was even more free from dissolved mineral matter. The specific gravity of a 

 sample from near the surface gave 1-00005 at 4° C. 



Irregular snow-drifts covered the surface of the lake. The particles of such snow 

 and neve, during the peculiarly warm conditions of summer and early autumn, " sweat " 

 together, forming a coarser granular mass, very much honeycombed. In the re- 

 crystallisation of snow standing on prismatic lake-ice, there is a strong tendency for the 

 prism structure to be continued above in the developing formation ; thus the ice-grains 



