CHEMICAL WEATHERING 199 



reaction are compounds containing ferrous iron, and the most probable products will 

 be limonite or haematite, causing the rocks to weather brown and red. It is a 

 curious coincidence (if it is not a result of the process) that the removal of snow- 

 drifts by ablation generally exposes a browner soil than the neighbouring perma- 

 nently-exposed soil. 



Although there appears to be very little chemical weathering at Cape Royds, 

 this is by no means the case in the districts examined by the Western Party, who 

 explored the Ferrar Glacier Valley, where this type of weathering seems to play a 

 much more prominent part in the denudation of present land-forms. In the moraines 

 its effect was especially important, and was brought before our notice in three ways. 

 The water of lakes of the Stranded Moraines, and that surrounding the boulders in 

 the moraines of the Ferrar Glacier, tasted very strongly of magnesium, and indeed 

 had a strong medicinal effect. The amount of salt it contained was especially 

 noticeable in the case of many dried-up lake beds in the New Harbour Dry Valley. 

 Where lakes had dried up owing to strong evaporation, their beds were covered 

 with a strong efflorescence of white salt. 



Many boulders of the more resistant types of rock represented in these moi'aines 

 were coated with a crust, in some cases an eighth of an inch thick, of carbonate of lime, 

 and the less resistant rocks, such as many of the softer varieties of Beacon Sandstone, 

 had had all their cement removed, and had become reduced in many cases to heaps 

 of individual quartz grains, whilst many blocks, although retaining some semblance 

 of their original form, crumbled to powder when struck with the haft of a hammer.* 



Plate LVI. Fig. 3 illustrates the effect of insolation in dissipating the ice 

 and snow from the surface of the dark kenyte rocks of Cape Royds, and Fig. 4 of 

 the same plate shows the general aspect of kenyte weathered spheroidally at Cape 

 Royds. 



DENUDATION AND EROSION 



A. By Avalanches. The descent of avalanches from the steep rock slopes of the 

 Antarctic Horst was observed by the Northern Party for a few days before Christmas 

 in the neighbourhood of Mount Crummer. At frequent intervals daily great 

 masses of snow would rush down with a deep thunderous roar on to the piedmont 

 ice at the base of the mountain. Such avalanches must of course move with them 

 a certain amount of rock material, but on the whole the denudation accomplished 

 by this factor is probably insignificant as compared with the erosion effected by ice, 

 running water, changes of temperature, and wind action. 



B. By Ice. Abundant evidence has already been quoted in support of the vast 

 amount of erosion accomplished by ice in this region of the Antarctic. This is 

 proved, both by the subtraction of material from the rocks of the horst, and the 

 addition of sediments to the floor of McMurdo Sound and Ross Sea. 



* Frost-weathering of course contributed to make these lumps of sandstone so friable. 



