LAKES AT CAPE ROYDS 153 



bottom of the lake, rose towards the surface, and accumulated under the sheet of ice. 

 The succeeding frost added to the bubbles owing to the air and gas in solution in the 

 water being expelled mostly above or below the new layer of ice formed. This frost 

 was evidently of a sufficient duration and power to add 3 inches of permanent ice to 

 the lake covering. The same process was repeated again and again, with the dif- 

 ference that as the non-conducting layer of ice on top of the lake increased in thick- 

 ness, and the remaining solution became more salme, the frosts, although becoming 

 more severe as the autumn approached, were unable to effect as much freezing of 

 the water as the earlier frosts, and thus each day's layer of ice decreased in 

 thickness until the daily variation of temperature ceased to have effect, and the second 

 uniform tyjie ice of ice (Type B.) began to form. 



Type B. This was the ordinary type of lake ice of uniform and slow growth. 

 The noticeable fact about the ice between 2 and 3 feet below the surface was the 

 gradual inception of the pseudo-fibrous structure and its analogy to sea ice. This 

 is, however, natural, for it is presumably due to the same reason as the fibrous 

 structure in sea ice, namely, to the extrusion of the salt as a highly concentrated 

 brine solution in a series of little globules, forming thermometer-shaped tubules, 

 outlining the ice prisms. 



Type C. The discoloured and odoriferous nature of this last ice is due to the 

 ice being saturated under pressure with a strong solution of gases in brine, the most 

 prominent ingredient in which solution is sulphuretted hydrogen, probably produced 

 by the decay of the algous material so common in all the lakes at Cape Eoyds. 



Mawson found that some of this brine solution froze at as low a temperature as 

 50° F. below freezing point. 



Temperatures. A series of temperatures taken in the trench is as follows. Mean 

 air temperature, June 24th, 25th, and 26th, was — 7"2^ F. 



The comparison shows a general but by no means uniform adjustment to the air 

 temperature. 



Second Trench in Green Lake, July Zlst, 1908. The section was as in the first 



