LAKES AT CAPE ROYDS 151 



The state of the surface changed considerably from time to time, for, although 

 generally rendered glassy and smooth by ablation, yet after a heavy blizzard before 

 the sea was frozen over the ice would be rendered very sticky by the sea spray ; 

 in fact the resemblance to a smooth sea ice surface was remarkable. Then, again, 

 after heavy blizzards portions of the lake near the shore would become covered 

 with snow. These drifts would persist for long periods before being removed by 

 ablation, and it was apparently on the underside of these drifts that the very 

 macrocrystalline prismatic lake ice was chiefly observed. Indeed the only places 

 on Green Lake where this form of ice was developed were those which were from 

 time to time covered by these drifts, although on other lakes, notably Clear Lake 

 and Blue Lake, the prismatic ice played a much more important part. 



By the contour of its basin there was reason to believe that this lake was 

 nowhere deep, and this belief was afterwards upheld by our trenching work. The 

 total depth of the lake at the spot where the shaft was sunk proved to be 6 feet 

 4 inches. 



Algous Deposit. There is practically no dejoosit on the southern shores of the 

 lake ; to the east it is scattered up the gravel slope for some distance, and pieces 

 occur many feet above the present level, but the sprinkling is very sparse except 

 for short distances along within 2 feet of the ice margin, where it is in places fairly 

 common. The principal deposit is at the north end. Here the width decreases 

 from a belt 12 paces wide at the north-east corner to one 6 paces wide at the north- 

 west corner, and three distinct ridges raised sharply 1, 2, or 3 inches high are well 

 marked at 3, 4, and 5i paces from the lake border. We believe these ridges to 

 be due to a combination of two causes. The presence of sparse fungus along certain 

 levels on the whole of the north and east side and half the west side of the lake 

 seems to indicate that these definite levels mark the surface of the ice at certain 

 definite periods of recession of the lake. On the other hand, the thick algous 

 deposit at the north, and particularly the north-west end of the lake, tends to the 

 presumption that it is due to the influence of the prevalent southerly winds in the 

 summer when the lake is thawed, and that the ridged appearance is due to wave 

 action, and this view was further strengthened by the way in which during a heavy 

 drift-laden gale in February 1909 the slush in the lake water was piled uja on 

 the leeward side of the lakes in similar ridges. 



Convexity of Lake Surface. On June 22nd it was noted that a main crack 

 running east and west had appeared at the southern end of the lake, and that the 

 ice to the south of this was tilted up towards the crack at quite a perceptible angle. 

 This convexity of the lake surface was, however, better seen and photographed in 

 some small tarns at Cape Barne, and will be dealt with under the Cape Barne 

 section. 



Trenches in Green Lake. On June 24th to 26th, 1908, the first trench was sunk in 

 Green Lake, and temperatures were taken by Murray at every 6 inches during the 



