and Suhaerial Denudation. 35 



to realize the rapid rate at whicli the rock is being destroyed, and 

 one has to experience the force of the wind adequately to estimate 

 its driving power from its set quarter. 



No one doubts that the strong S.S.W. wind has been the agent 

 by which a natural concentration of the diamonds in the valleys 

 of the Liideritzbucht district has been brought about, a concentration 

 which has made their exploitation economically possible. As the 

 diamonds have not been shown to extend very far inland it has been 

 thought by some that marine agency has had something to do with 

 their occurrence. It has been pointed out that the coast is under- 

 going slow upheaval, and that diamonds have been found in the 

 material of the " raised beaches " which terrace the hills in certain 

 of the valleys of the littoral. But as to this there seems to be no 

 reason why the enrichment should not have taken place from a 

 landward area, and not necessarily from seawards. 



It is quite likely that the S.S.W. wind may be entirely responsible 

 for the denudation of the parent diamond-bearing rock as well as 

 for the concentration of the diamonds after being set free. The 

 occurrence of the diamonds near to the sea is probably due to the 

 fact of the denuding agent being a coastal wind. This coastal wind 

 occupies a stratum which does not reach to any considerable height 

 into the atmosphere. As one proceeds inland the country rises 

 fairly ra|)idly. In the experience of the writer it may be blowing 

 a gale at Liideritzbucht, while at Haalenberg, 33 miles inland by 

 rail, and considerably less as the crow flies, the air may be nearly 

 still. Haalenberg is 1,816 feet above sea-level. An arborescent 

 aloe, Aloe dichotoma, common in the interior, comes down to about 

 this neighbourhood. It does not reach the coast, it could not with- 

 stand the wind, although there are switch forms of vegetation 

 which can bow before the wind, and lowly plants, mostly of fleshy 

 habit, which can win their way as far down as the sea. It would 

 seem that we have in noting the habitat of such arborescent forms 

 as Aloe dichotoma a guide to the limitations of the coastal wind 

 in both vertical and lateral planes, and consequently to the area 

 the denudation of which has furnished the diamonds. 



The hifls lying inland between Liideritzbucht and Kolmanskop 

 are of metamorphic rock, and in general resemble the Diamantberg. 

 They are not high, and one hill is very much like another. Very 

 curiously the broad effect of the landscape in this region is suggestive 

 of a terrain which has been swept by an ice-sheet. There are the 

 generally rounded outhnes, the hummocky effects. The resemblance 

 must be illusory, for subaerial denudation is going on so rapidly 

 that one judges the outlines to have been comparatively recently 

 imposed. The directional trend of the sand-blast may be responsible 

 for the likeness. 



