SCIENTIFIC RESULTS 



we stayed there. A geological result of this overflow of 

 cold air from the inland plateau is that several beautiful 

 instances of mechanical weathering through the agency 

 of the sand blast are to be seen. The most marked in- 

 stance of this type of weathering was to be seen in 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 large cocoanut to that of an ordinary glass 

 marble. 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 sand- 

 stone was found which proved to be full of round patches, 

 anything up to half a foot in diameter, which were of a 

 difPerent colour and consistency from the rest of the 

 rock. Several of these round nodules had weathered out 

 and were lying at different distances from the parent 

 rock, and when one or two of them were collected and 

 broken across the middle with a hammer they were seen 

 to consist of a very hard and indurated outer shell from 

 an eighth to half in inch thick, enclosing a dark green 

 ferruginous-looking sandstone of larger grain and with 

 less cohesion between the grains. The mode of origin of 

 these structures was now clear for they were to be seen 

 in all stages of formation from the nodule which was 

 left intact and only polished on the outside, through the 

 various intermediate stages, to the perfect cup where the 

 inside had been completely cleaned out and only the 

 polished outer shell was left, containing many of the 

 quartz grains which had been used by the wind as a file 

 to get rid of the less resistant portion of the stone. Even 

 a further stage was to be seen, for in time the outer shell 

 itself began to wear away and the cup became sufficiently 

 light to be moved by the wind and many had been lifted 

 up and smashed to pieces. 



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