WIND WEATHERING 197 



small it is true, but many of them, on the contrary, are quite large. Several 

 members of the Expedition were struck quite heavy blows by the gravel carried 

 from the ridge behind the Hut during some of the blizzards, and pieces up to an 

 inch or more in diameter have been found on the fast ice at distances from the 

 cliffs, which they could have traversed in no other way. 



A local effect, but one which must have an appreciable effect off the great 

 rookeries, is the removal of the fine guano dust by the powerful blizzards of the 

 spring. The long ablation during the winter and autumn had caused the accumula- 

 tion of a lot of loose dust on the Cape Royds Rookery by the end of the winter of 

 1908, and the first spring blizzard removed the majority of this. There may have 

 been some slight difference in the direction of this wind, which miglit account for its 

 removing so much of the material which had apparently been almost untouched by 

 previous blizzards, but whatever the cause, the effect was very obvious. The 

 whole of the drifts to the north of the rookery were coloured a deep brown, the 

 fast ice of the Sound was discoloured until it came to an end at Blacksand Beach, 

 large quantities of the dust must have been carried right out to sea, while behind 

 every projection along the coast the snow-drifts were discoloured, and it was 

 impossible to get away from the unpleasant, penetrating smell of the guano any- 

 where to the north or north-west of the rookery. 



In the Ferrar Glacier Valley denudation by wind was not so common as at Cape 

 Royds, but locally it was very active, owing to the influence of the plateau winds. 

 The reason for its influence being less in this valley is not so much that the winds 

 are less, as that the amount of fine gravel which would be used as an agent of friction 

 is insignificant. Such material as is carried on to the surface of the glacier by the 

 winds is either removed by the thaw into the streams, which in their turn carry it 

 to the entrance of the valleys, or is swept by the wind into the channels of the 

 super-glacial streams and lodges there, or jJerhaps, if left long on the surface of the 

 ice, becomes embedded there, and finally disappears beneath the surface. A limited 

 amount of wind-weathering shows in some of the boulders of the moraines, and 

 where it does occur the weathered surfaces all point up the glacier, so that evidently 

 the strongest and most common winds here met with are those which are caused by 

 the downward overflow of the cold air from the plateau. 



It was in the gully between Knob Head and Terracotta Mountain that the most 

 striking instances of weathering of the sand-blast type were to be seen. One was 

 the occurrence of numerous cups of sandstone beautifully polished and concentrically 

 striated on the outside and hollowed out more or less perfectly inside, ranging in 

 size from that of a cocoanut to that of an ordinary glass marble. (See Plate LVII. 

 Fig. 3.) We were for some time puzzled to account for the origin of these "pot- 

 holes," as we named them, but the mystery was cleared up when a block of 

 weathered sandstone was found which proved to be full of rounded patches, anything 



up to I a foot in diameter, which were of a different coloin- and consistency to the 



2 c 



