ECONOMIC GEOLOGY 471 



patches with a heavy over-burden, or handicapped by 

 absence of water-supply, which are likely to be treated 

 in the future. 



The source of the diamonds in these alluvial deposits 

 has given rise to some controversy, inasmuch as the 

 gems differ to a certain degree from those obtained in 

 the pipes hitherto worked, and for this reason they have 

 even been considered as derived from the Pniel amyg- 

 daloidal diabase of the Vaal Kiver Valley, 1 though this 

 view seems rather improbable. 



Diatomite or diatom-earth has been found in certain 

 pans in Bechuanaland and Griqualand West, e.g., 

 Witkop in Gordonia, and the pan on Craigie Burn near 

 Belmont (Herbert). This material is probably not un- 

 common, but, in the midst of white calcareous tufa 

 which always accompanies it, its presence is usually over- 

 looked. 



Gold. Auriferous veins have been found in the 

 Kraaipan formation 2 in Mafeking, at Madibi and *at 

 Kraaipan. At the former locality the reef which is 

 being worked occurs in chlorite- and calcareous-schist 

 and contains quartz, chlorite, calcite, pyrrhotine and 

 pyrites. Generally speaking, quartz veins in the granite 

 and in the massive banded ironstone have proved to be 

 barren. Some of the cherts and granulitised quartz 

 veins carry several pennyweights of gold in various 

 localities. In Knysna 3 the Millwood goldfields lie 

 among the Outeniqua Mountains, which are made of 



1 H. Merensky, T. G. S. S. A., x., p. 107. 2 G. C., x., p. 230. 



3 E. H. L. Schwarz, G. C., x., p. 86 ; and G. M., p. 369, 1905. 



