326 Reviews — P. A. Wagner — South African Geology. 



Lastly, I may mention that in 1907 I was favoured with a visit 

 from the late Professor Dr. Gottsche, Director of the Hamburg 

 Museum, and one of the chief authorities on the molluscan fauna 

 of the North German Miocene deposits, for the purpose of examining 

 the Lenham Collection of the Museum of Practical Geology, which 

 was then in my keeping at the British Museum ; he was specially 

 interested in some specimens referred to in Mr. Beid's memoir as an 

 elongated variety of Triton heptagonum (?), being confident that they 

 represented Beyrich's Fusus sexcostatus, a characteristic fossil of the 

 Upper Miocene formation of North Germany. He was further of 

 opinion that the Lenham Beds were older than had hitherto been 

 supposed, and he considered that they should be referred to the 

 Miocene period. 



IRZE^IIEWS- 



1. — Some Problems in South African Geology. By P. A. 

 Wagner. Proc. Geol. Soc. South Africa, 1917, pp. xix-xxxix. 



IN his Presidential Address to the Geological Society of South 

 Africa for 1917 Mr. P. A. Wagner dealt at some length with 

 four outstanding problems of the geology of that country, namely, 

 the origin of the gold-reefs of the Band, the genesis of the diamond, 

 alteration of diamonds after their formation, and the nature of the 

 famous salt pan near Pretoria. On each of these he had something 

 of interest to say. An excellent summary is given of recent views as 

 to the source of the gold in the Banket. Dr. Mellor has recently 

 brought forward evidence in favour of the "placer" theory, founded 

 largely on the actual distribution of the gold in the conglomerates. 

 It is found by assays that the gold is richest where the pebbles are 

 largest, and it is therefore argued that the gold was deposited by the 

 strong currents that brought the large pebbles, the weaker currents 

 that could bring only the finer sand not being competent to carry 

 the heavier grains of gold. Nevertheless, the actual character of the 

 particles of gold indicates recrystallization in place. Mr. Wagner 

 dissents from Dr. Mellor' s view that the quartzites and conglomerates 

 were deltaic deposits and regards them as having been formed on 

 beaches in a subsiding area. 



The author considers kimberlite as the hypabyssal or volcanic 

 form of a peridotite magma which he believes to underlie the granitic 

 and other rocks at a great depth, and he regards the diamonds as 

 original constituents of this magma, brought up, often in a fragmented 

 form, during extrusion. He also gives some facts of great interest as 

 to the possible effect of radio-activity or other agencies on diamonds 

 after they reached their present position. This subject, however, 

 appears to be of a very speculative nature, and much work is 

 obviously required. 



The salt pan on the farm Zoutpan, 25 miles N.N.W. of Pretoria, 

 now gives rise to - a considerable industry. The pan itself is a most 



careful rubbing down of the horizontal surface on the median plane of the 

 figured example, there is exposed a series of minute chamberlets of squarish 

 or hexagonal outline which can only belong to the Miocene genus Lepidocyclina. 



