LAKES AT CAPE ROYDS 163 



This series of temperatures was taken at a time when there had been a sudden 

 and considerable rise in the air temperature, and the apparent inconsistence in the 

 temperatures respectively at 1 foot and at the surface is due to the gradual adjust- 

 ment of the ice temperatures to the new air temperature. The slowness of heat con- 

 duction in the lake ice is very well seen here. 



Other Trenches m Coast Lake. April 1st. A bore was put down in Coast Lake 

 along the main crack which formed one side of the trench already described, but a 

 few yards farther from the sea and as near to the centre of the lake as possible. 

 There was 2 feet 3 inches of ice, and the depth of the lake was nearly 4 feet. Very 

 little bottom material was obtained. It was in this bore that a bamboo was fixed a 

 few days later, by means of which the amount of ablation from the lake surface during 

 the next few months was measured. 



August lOth. A second trench was put down in Coast Lake. The section was 

 very similar to the preceding, and the alga was struck at 1 foot 6 inches and proved 

 for a foot. 



August llth. A third trench was sunk in Coast Lake, when the algous peat 

 was reached at 2 feet 3 inches, and again proved to be more than a foot thick. 



During the spring powerful ablation exposed large stretches of this algous peat 

 deposit near the edges of the lake, so that there is reason to believe that almost 

 the whole of the lake bottom is covered with it. The ice of Coast Lake was 

 traversed by a series of contraction cracks, and the surface of the ice was distinctly 

 convex in places. These cracks opened on cold nights with a sharp loud tang, 

 something like the sound made by the cracking of a stockwhip. Mawson estimated 

 that on June 20, 1908, the minimum amount of contraction of the ice as shown by 

 the cracks was 10 inches in a horizontal distance of 150 yards. The contraction 

 amount was evidently much more, but was masked by the secondary addition of ice 

 to the walls of the cracks, derived from vapour steaming up from the water below. 



Round Lake. This small tarn occupies a depression between Blue Lake and 

 Clear Lake, but is of the Green Lake and Coast Lake type. A trench was sunk 

 in it on April 17th. At about 2 feet 3 inches we reached the bottom, and broke 

 through a thin layer of decayed alga into the gravel beneath ; for some time before 

 reaching this layer, however, its presence was advertised by the unpleasant smell 

 of the gases liberated and the yellow colour of the ice. The ice all through was 

 characterised by a streaky appearance, owing apparently to the extrusion of salt 

 solution globules between the crystals. 



Temperatures. 



Surface . .' -1.5° F. 



Depth 6 inches - 12° F. 



„ 1 foot - 9° F. 



„ 18 inches - 5° F. 



„ 24 „ 0° F. 



Air temperature . . . . . . . . - 25° F. 



Y 



