DENUDATION 195 



fell directly on the moving ice face, high screes of detritus were piled. These screes 

 in some cases must have reached two or three thousand feet in height, and practi- 

 cally the whole of the material of the upper portion of them must have been derived 

 from the frost-weathering of the cliff faces, for in such situations the action of 

 torrential water must be negligible. The lower portions of these screes contain large 

 quantities of rock which cannot have been derived from the cliffs above them, and 

 must be the material which formed the lateral moraine of the glacier at a former 

 more extensive phase of glaciation. 



A jjhenomenon due to sudden change of temperature was observed during our 

 stay at the Christmas Camp below Knob Head Mountain. During the whole of the 

 stay we met there a very cold breeze, the overflow of the heavy air from the Inland 

 plateau, which was blowing over the ice in the neighbourhood of the tent. In the 

 evening we usually lost the sun about half-past nine, and immediately the shadow 

 of the moimtain swept across the ice near us the ice was suddenly cooled by the 

 wind, and repeated sounds of sharp cracking would be heard, the cracks taking the 

 form of minute strain lines in the surface of the ice. This action was much more 

 marked in the case of the thin layer of ice covering the boulder holes containing 

 thaw-water, for these layers immediately contracted with reports like a succession 

 of pistol-shots, and sometimes broke up altogether and flew out in all directions, 

 making a noise like breaking glass. 



3. Due to Wind Weathering. The effect of the sand-blast action on different types 

 of rock was very well seen at Cape Royds, covered as the peninsula was with large 

 and small erratic boulders of almost every description and texture. In the kenyte 

 the porj^hyritic anorthoclase felspars were more resistant than the ground mass, and 

 stood out all over the rock like iron studs in old-fashioned doors. The wind weather- 

 ing of tlie kenyte will be more fully described in the Cape Barne section, for it 

 was at the latter place that the best local boulder was seen and photographed. 



Plate LVII. Fig. 1 shows a piece of kenyte, a third of which was embedded in 

 the ground, and protected by the gravel covering it, so that the weathered portion 

 is standing on a natural pedestal. The contrast between this pedestal and the rest 

 of the block gives one a very good idea of the way the felspars stand out in the wind- 

 carved surface, and when it is realised that practically the whole of the exposed 

 kenyte surface is of this description, the roughness of the country can be fairly 

 well gauged. 



When there were any lines of weakness in the boulder, for instance, lines of flow 

 in eruptive rocks, or lines of stratification in the Beacon Sandstone, the sand worked 

 much more quickly along these lines, and the rocks were given the appearance shown 

 in the second figure. One specimen of variolitic basalt was reduced to a rim of rock 

 half an inch thick, enclosing a space, about four inches by three, occupied by a series 

 of round balls about three-eights of an inch in diameter, and almost completely 

 weathered out, so that the individual varloles might have been broken off by the 



