20 AUSTRALASIAN ANTARCTIC EXPEDITION. 



The ice front of the glacier rises very steeply to the south, and, for a vertical thickness 

 of 40ft. above the rock floor, the ice is coloured brown by the presence of subglacial 

 rock detritus (Plate XXXI. , fig. 1). Similarly to the east and the west of Cape Denison, 

 whenever the ice cliffs rest on a rock basement, brown-coloured ice could be seen for 

 estimated thickness of 15ft. or 20ft. (Plate XIV., fig. 2). The ice sheet, therefore, has 

 at this point eroded the underlying surface. In this connection it is interesting to recall 

 the observation of a sledge party, 20 miles to the east, to the effect that rock outcrops 

 at this distance away are found to be nearly devoid of morainic material, though the ice 

 sheet is continuous and unbroken. A paucity of erratics has also been noted by Sir 

 Douglas Mawson at Cape Hunter, nine miles west of Cape Denison. The area of abundant 

 glacial debris is, therefore, limited in Commonwealth Bay. 



The subglacial material (Plate XXX., fig. 1) consists of fine rock meal, grit, 

 pebbles, and boulders, some of the latter weighing many tons. For the greater part 

 of the year it is all part of a hard-frozen zone, but the summer thaw loosens a good deal 

 of surface material. The yearly ablation also liberates a certain amount. The finer 

 material is, as above stated, swept away by the winds, and no glacial soil or gravel, 

 except in isolated cases, can remain exposed. The exposed surface thus presents an 

 aggregate of boulders of all sizes and shapes. 



The moraines are, for the most part, thickly banked up in lines parallel and near 

 to the glacial front. They contain a great variety of rocks which are not found in situ, 

 and are, therefore, known to exist hidden beneath the ice cap. Among these rock types 

 are crystalline limestones, lime silicate schists, sandstones and quartzites, granites, 

 dolerites, vein and pegmatitic material, and schists and gneisses in great variety (Plate 

 XIX., fig. 2). In general there is a great similarity between many of our specimens 

 and those reported from the Ross Sea area by the Scott and Shackleton expeditions. 



In the field it was found convenient to recognise an " upper moraine " and a " lower 

 moraine." The " upper moraines " are true moraines, formed in the manner indicated 

 above. It is the usual type of deposit with many of the stones much worn, though 

 not often well rounded like river pebbles. Some look like rock chips with the salient 

 angles and edges worn off. Many are subangular with plane and bevelled faces, and 

 a small percentage (possibly % per cent.) are striated. The " lower moraines " are not 

 strictly moraines at all. They do not occur above the 40ft. contour level and contain 

 a very large percentage of local rock. 



The abundant variety of rock types on the " upper moraines " makes them very 

 different from the "lower moraines." In the latter the boulders are more rounded 

 (Plate XIX., fig. 1), though still not altogether like river or marine boulders ; many 

 have plane, bevelled, gouged, and polished faces, but very few are striated. Further, 

 some degree of sorting into sizes seems to have been accomplished. Some banks are 

 dominated by boulders averaging one foot in diameter ; while others consist, in the 



