196 GENERAL GEOLOGY 



hand. One type which was sufficiently common to deserve notice was a basalt with 

 much altered olivines and strongly cleaved augites. Both these minerals, being 

 apparently easily disintegrated, had disappeared almost entirely from the surface of 

 the rock, leaving what was apparently a homogeneous basalt full of small pits. 



Lastly, the kenyte tuffs with a soft ground mass had in some cases had this 

 ground mass removed so much that numbers of the kenyte fragments might be seen 

 lying loose around the tuff blocks, and only to be recognised as having been originally 

 part of the block by the presence of a little of the cementing material still adhering 

 to their leeward sides. 



The power of this tyjse of sub-aerial denudation must be greatly added to at 

 Cape Ptoyds and Cape Barne — in fact at any place where the country rock is kenyte — 

 by the quantity of small undecomposed fragments of felspar that are lying amongst 

 the debris. The anorthoclase felspars of the kenyte are liberated in immense 

 numbers by the weathering of the rock, and they are liberated in an undecomiwsed 

 state owing to the excess of mechanical disintegration over chemical alteration. 

 This excess is mainly due to the absence of much water denudation. 



These felspars, owing to their perfect cleavage, are easily broken up into small 

 pieces, and are carried by the wind against the face of other rocks, every fragment 

 acting as a small but sharp chisel. When these felspars, for instance, are hurled 

 hard against any obstacle, the resistance does not cause a blunting of the point so 

 much as a splitting into smaller cleavage masses, thus doubling or trebling the 

 number of sharp points. 



The presence of these immense numbers of undecomposed felspars, large quantities 

 of which are carried out to sea as fine dust, and similar large quantities removed in 

 larger pieces by the floe-ice and ice- foot bordering the coast, must be having a 

 marked effect on the beds at present forming under the Ross Sea, and partially 

 decomposed sub-angular and angular pieces of felspar will be an important factor in 

 the rocks which these beds will form when finally consolidated.* 



Another way in which the winds are playing an important part in the denuda- 

 tion of Ross Island is presented when we consider the quantity of fine material 

 which must annually be deposited in the Ross Sea, having been removed by winds 

 from the peninsula. We have already mentioned in our notes on ablation how, 

 towards the end of October, the whole of the sea ice beyond Cape Barne became 

 dirty with sediment ; and all that material must have been deposited in the sea when 

 the ice melted. The fine dust from Cape Royds, and a good deal of fairly coarse 

 material too, must be removed straight Into the sea to the north. It is necessary 

 that we should not give the idea that the size of the individual grains removed in 

 this way are all microscopic. By far the greater proportion of the grains are very 



* It is well known that undecomposed felspar fragments are very characteristic in the glacial 

 sandstones of Cambrian age in South Australia, as well as in the Permo-Caiboniferous glacial sand- 

 stones and tillites of India and Australia. 



