16 AUSTRALASIAN ANTARCTIC EXPEDITION. 



the broad outlines of rounded bosses of rock are always indicative of glacial planing, 

 but in minute detail the surface is usually found to be minutely pitted and roughened 

 by the unequal erosion of the constituent minerals. Nevertheless polished and striated 

 surfaces can be discovered, and one block about 9ft. square with long, well-marked, 

 parallel striae was photographed (Plate XVIII., fig. 2). The striae trend N. 32 E. 



The existence of a lower zone of relatively polished rock and a higher zone of 

 relatively unpolished rock is a noteworthy feature. It is believed that the roughnesses 

 on the surface of the rocks is due to abrasion of millions of snow grains. In this case 

 the upper zone must have been exposed for a longer time than the lower (below the 

 40ft. contour), which has been relatively protected. But the shore line is capped for 

 almost the whole year by an ice foot, which is stationary and protective, and wave 

 erosion has only opportunity for limited action. The ice foot is usually about 15ft. 

 high, and may provide a simple explanation of the preservation of the well-polished 

 surfaces on the border zone of land and water. Then if we assume a slight relative 

 and recent uplift we may easily explain a relatively protected zone up to 40ft. 



The highest point of the Mackellar Islands is about 40ft. above sea level, and the 

 notes made by Sir Douglas Mawson show that the character of their surface is the same 

 as the peripheral area of Cape Denison. Though no highly polished surfaces or striae 

 were found, the general surface of the islands is flat and in part very smooth, with the 

 prominences well rounded. Roughnesses can be explained by very recent disintegration. 



Glacial plucking is evident. When the glacier has passed over a sloping resistant 

 rock face the lee side is often found to be steep, because the rock has been plucked out 

 by the onward travel of the ice. 



Lakes. Five small glacial lakes are present in this area, and theii position is shown 

 in the locality plan, and their manner of occurrence is illustrated in Plate XXXI., fig. 2. 

 Four of these are almost round in shape and 30yds. to 40yds. broad. Lake II. is not 

 quite so broad, and its length is more than three times its breadth (Plate XVII., fig. 1). 

 We mention this point because the direction of the glacial movement has not 

 corresponded with the long axis of the lake. Lakes III. and V. (Plate XX., fig. 1) 

 are situated on valley floors, while Lake IV. (Plate XX., fig. 2) is on the highest level 

 about 120ft. above sea level. Lake IV. is bounded on the northern side by a rock 

 wall thickly banked with morainic material (Plate XXL, fig. 2). The lakes average 

 about 20ft. in depth, and they represent depressions gouged out of the rock floor by the 

 forward movement of the ice. 



Valleys. There are four parallel, broad-bottomed, shallow valleys. In parts 

 their sides are moderately steep, and their trend is N. 15 W., which is very nearly 

 coincident with the strike of the rocks (N. 4| W.) (Plate XV., fig. 2, Plate XVII., fig. 2). 

 This direction makes an angle of 45 with the direction of the trend of the glacial striae, 

 and the origin of these valleys is an interesting problem which will be introduced after 

 other sculpturing factors have been discussed. 



