1889.3 Formation on the South West Coast of Africa, SfC. 327 



really only polished by the constant attrition of the smaller particles 

 blowin against them. Radiation from this glistening surface 

 and its bordering sand hills is necessarily very great, and as soon 

 as the sun rises the air becoming heated begins to ascend. 

 This action increases as the day advances and the heat becomes 

 greater; and daring the summer months, when the air over the 

 sea is much colder and denser than that of the interior behind 

 the desert, a current from the ocean is introduced to fill the vacuum 

 caused by the ascending air. This action, increasing as the 

 radiation increases, and decreasing again as the sun sinks, 

 is the cause of the rise and fall of the South-west wind so prevalent 

 in summer. Again, as all the rain in these parts comes in the form 

 of afternoon thunderstorms from the North-east and falls from 

 November to May, it follows, and actual observation verifies the 

 theory, that these South-west winds day by day drive back the 

 approaching rain clouds, which may be seen banked up and dis- 

 charging their contents to the eastward where the power of the 

 South-west becomes less as the distance from its generating causes^ 

 the desert and the sea, increases. Thus a reciprocal action is in 

 force ; the want of rain to check denudation, by the winds, of the- 

 decomposing rocks and to promote the growth of vegetation causes 

 the desert, the radiation from which creates the South-west current ;- 

 while this same South-west wind, by driving back the rain continues 

 the conditions which result in its own formation ; consequently there 

 is but little hope of any improvement in the condition of this waste, 

 which is also so saline as to render afforestation or cultivation next 

 to impossible ; it will, therefore, probably remain a desert as long 

 as the present geological conditions remain unchanged. 



When, as is the case at intervals during the winter months of 

 May to October, the evaporation after the rainy season generates 

 sufficient cold to reduce the atmospheric temperature of the country 

 behind the desert to a point lower than that of the sea, a reverse 

 action is set up and wind from the East rushes in to fill the daily 

 vacuum caused by the rise of the air over the heated desert ; and 

 when, as also happens at intervals, the night temperature of the 

 interior falls below the freezing point, coincidently with clear weather 

 near the coast, this wind increases to a powerful gale. Cold at the 

 eastern fringe of the desert it becomes warmer as it passes over the 

 heated surface, till at the coast it is a scorching sirocco. It carries 

 with it enormous quantities of dust resulting from the disintegration 



