LAKES AT CAPE ROYDS 161 



C. From 9 to 11 feet the ice contained a quantity of living alga with living roti- 



fers and water-bears, and frequently around the pieces of alga we could 

 observe a circular jsatch of ice which was quite opaque, evidently owing to 

 secretion of some substance from the plant. 



D. At 1 5 feet bottom was reached, consisting of a breccia of keny te and gravel 



formed from this rock, together with numerous small erratics cemented by 

 ice, and containing a considerable quantity of both living and dead alga. 

 One fi-agment worthy of note was an angular piece of trachyte, coated on 

 both sides with a layer of growing alga. This alga, when examined by 

 Murray, yielded numerous colonies of a smaller unicellular alga with abun- 

 dant chlorophyll, several rotifers and water-bears, and a mite. 

 It seems that the bottom of the layer C. must be the downward limit of the effect 

 of the summer thaw of recent years, and it must be very unusual for the thaw to 

 extend even to that depth, for within the range of our experience there has been 

 very little even of surface thaw at this lake, the removal of the surface of the ice 

 being almost wholly confined to ablation of the nature of evaporation. Unless melting 

 takes place from the bottom upwards, it must be very rare for the whole of the lake 

 ice to be thawed, and the presence of living algfe and microzoa at this depth is thei'e- 

 fore very interesting, for the period of suspended animation in both plants and 

 animals must extend over many seasons. A very mild summer indeed would be 

 necessary to cause much of the Blue Lake ice to melt, for this lake is of much greater 

 bulk than the others of the peninsula. A factor still more potent to preserve the ice 

 is the snow-covered nature of the slopes immediately bordering the lake. It is only 

 locally in the shallower parts of the lake, where the insolation of the kenyte is pro- 

 nounced, that any large amount of ice is thawed. 



OTHER TRENCHES IN BLUE LAKE 



Trench sunk in the Narrows of Blue Lake, Julij 20th. The ice was only 3 feet 

 thick, and the section was as follows : — 



A. 3 inches of ice, with very coarse gas bubbles partially filled with powdery ice. 



B. 6 inches of ice, in which the bubbles were drawn out into fine capillary tubes. 



C. 2 feet 3 inches of very clear and compact ice, with conchoidal fracture, and 



apparently very pure and free from bubbles. 

 Through all three varieties a coarsely prismatic structure was very marked, the 

 ice being crystallised in long hexagonal prisms about half an inch in greatest trans- 

 verse diameter, the outlines of which could be traced through the two upper types 

 of ice, and the first 6 to 18 inches of the third type. This ice must have been the 

 product of the freezing of last year's thaw-water, for even in the summer 1908-9 

 (an exceptionally rigorous one) this portion of the lake ice was completely melted. 

 Mawson reports that the ice at this spot is slightly saline. 



