THE GEOLOGICAL FORMATION OF GERMAN S.W. AFRICA. 339 



Of Ihese coarser particles further concentration takes place on 

 account of the difference in weight of similar sized particles of 

 different minerals. The mixed debris which has gradually found 

 its way to this locality, contained also diamonds from the nearest 

 pipes and the gravel which now remains is naturally far richer in 

 diamonds, this mineral being about 35 per cent, heavier than most 

 of the other particles with which it has been associated. 



This seems to be a simple and natural explanation of the 

 presence of the diamonds, though several different theories have 

 been advanced. 



It would be idle to speculate on the probable position of the 

 pipes from which ihe diamonds were derived, for the simple reason 

 that it is very unlikely that the various agencies that have in- 

 fluenced the removal and concentration of loose material, were 

 always the same as we now observe them. For instance, one can 

 readily understand that if at any period of the earth's history the 

 great extent of inland country to the east and south-east of 

 Luderitzbucht were not covered with soil, but resembled the coastal 

 belt, diaiTionds may have been transported for many hundreds of 

 miles in the same way as they are at present being shifted in the 

 neighbourhood of Luderitzbucht. 



Again, if at any time the axis of the earth had occupied any 

 other position than its present one, the direction of the trade winds 

 would have been different and the w-ind transportation would have 

 taken place in quite a different direction. 



In conclusion, I would emphasise the futility of laying down 

 hard and fast theories founded on the observation of the present 

 day condition of the earth's crust. 



In geological history time and space are practically illimitable. 



Our knowledge of the Earth's crust is indeed very limited. We 

 live on the surface and here or there we dig or scratch and draw 

 pipes, it seems a safe conclusion to come to that the number still 

 conclusions from what is revealed to us. A very large proportion 

 of the rocks forming the crust is covered with soil, and we remain 

 in profound ignorance of what is beneath. 



But since our more or less random diggings and scratchings 

 have revealed the existence of a large number of diamond-bearing 

 pipes, it seems a safe conclusion to come to that the number still 

 undiscovered must be very large indeed. The discovery of some, 

 much nearer to the Luderitzbucht deposits than those at present 

 known seems well within the bounds of probability. 



MAIZE INDUSTRIES.— In a recent issue of the Chemi- 

 ker Zeitung', an account is given of Doby's investiga- 

 tions into the possible productiveness of maize as a source of 

 sugar, cellulose, and alcohol. In Germany, although the culture 

 of maize proves profitable, the proportion of sugar is lower than 

 in America. The amount of sugar may be increased by remov- 

 ing the young cob before the seeds ripen. For the manufacture 

 of paper the stems, leaves, and axis of the cob are of value, the 

 unripe cobs and the green stems being capable of yielding alcohol. 



