and Subaerial Denudation. 33 



an admirable instance of seolian denudation. It is a desert area, a 

 region of rock and sand. The average annual rainfall is 0"78 in. 

 There are no running streams. Water for drinking purposes must 

 be imported or distilled from sea-water. 



The rocks are of the ancient metamorphic complex, so wide- 

 spread over the Protectorate. A confused medley of granite, aplite, 

 gneiss, and schists. There is much commingling of types as a result 

 of injection, pressure, and earth-movement. 



Overlooking the town of Liideritzbucht there is a rocky eminence, 

 known locally as the Diamantberg, which within an area of a square 

 mile or so shows many types. The prevailing one is, perhaps, a 

 biotite-schist, which in many places has been invaded to a varying 

 degree by granite or by aplite. The difference in colour between 

 the schistose and the granitic elements shows up the degree of 

 admixture very clearly. In some places masses of schist are to be 

 seen uninyaded by granite, in others masses of granite or of aplite 

 occur without trace of schist. Here and there are large segregations 

 of quartz. Veins and eyes of felspar are common. The rocks are 

 exposed uj)on every side, for there is no vegetation that counts 

 to mask or protect them. 



Although the rainfall is so small the country is carved into hill 

 and valley, and ravines course down the steeper slopes. The floors 

 of the valleys are occupied by mixed sand and grit, a fluent medium, 

 which is disposed much as water would be in a non-desert area, 

 broadening as the valley opens out, narrowing as it closes in like 

 a sand river-bed, which frequently provides the most convenient 

 highway for man and beast. Heat by day and cold by night have 

 their due effect no doubt, but it is the wind which is mainly 

 responsible for the large quantities of rock- waste and debris which 

 litter the surface upon all sides, and for the honeycombing the 

 rocks have so frequently undergone. 



The great destructive wind of this area blows from the S.S.W. 

 It is a seasonal wind blowing from October until April. Years ago 

 Andersson noted its effects upon the habits of certain birds. Perhaps 

 only a light breeze in the morning, it rises to a gale in the afternoon, 

 dying down again after nightfall. From time to time there are 

 calm days. It is a wind laden with salt and with moisture where 

 it first strikes the land ; thereafter it lays the desert under tribute, 

 and armed with grit and sand scours everything in its path. 



No rock entirely withstands the attack. Effects vary. It is rather 

 curious to see how in large boulders, say, of granite, apparently 

 of even texture throughout, one portion of the mass may be merely 

 dull polished and lightly scooped out, whilst another portion is 

 deeply bitten into. 



The biotite-schist shows the ravages conspicuously. The rock 

 is pitted, riddled, and holed, with " worm-eaten ", honeycombed 

 effect. It rots away. Near to the sea, no doubt, the salt in the air, 

 owing to its chemical reaction with the ferruginous element of the 

 schist, adds to the destructive effect. 



VOL. LVII. — NO. I. 3 



