224 s i:\VA (•.!■: i-low and \\aii;k siitia. 



a bait million galk)iis. or 3.19% greater tlian the tiow during- the 

 iiionth of niininnini consumption. The deduction, therefore, is 

 that it is quite reasonable in designing the sewage sjfstem for a 

 town climatically similar to jobannesbiu'g. to base its capacity 

 upon the minimum water cousupi])tion plus, say, a 15','r increase, 

 to allow for a factor of safety. 



The South African Diamond Fields. — Dr. 



Wagner's recently published book* is a most valuable account of 

 the geological and economic aspects of the diamond fields of the 

 Union, Rhodesia, Cierman South-W est Africa, and the Belgian 

 Congo. The author has had a large experience in the mines and 

 diggings, and has a tht^rough knowleilge oi the results obtained 

 by other geologists who have investigated various i)arts of the 

 subject. The long table of contents, the numerous references in 

 the text, and the excellent list of previous ])ublications will enable 

 readers to follow up almost every detail in the geological side of 

 the subject, l)ut the lack oi an index is a great source of incon- 

 venience. 



The discussions of the many geological problems raised by 

 the diamond-bearing rocks are marked by their fairness to all 

 previously expressed views and by their sound common sense. 

 The greatest ditficulty in the petrology of the original deposits is 

 due to the fact that the rocks are unknown in an unaltered state, 

 and there are no signs that new discoveries will remove this 

 difficulty. 



The first chai)ter deals with the habit and general characters 

 of the rocks known as kimberlite ; in the second there is a very 

 useful and complete account of the minerals which occur in 

 kimberlite ; in the third chapter the petrogra])hy of all the known 

 varieties of kimberlite is described, as well as of other rocks 

 which there is reason to think were genetically connected with 

 them, the concluding section being devoted to speculations on the 

 possible connection of the eruption of these deep-seated rocks 

 with the event which resulted in the elevation of the sub-con- 

 tinent in late Cretaceous or Tertiar\- times. 



The fourth chapter deals with the extraordinarily interesting 

 xenoliths which are evidently related in origin to the kimberlite 

 containing ihem ; in the fifth chapter the (liamond is described, 

 the characteristics of the stones got from different mines, and 

 there is a careful discussion of the various views as to the origin 

 of the» diamond, which the author shows has probably crystallised 

 in the magma that gave rise to kimberlite while it was deep down 

 in the earth's crust. 



The next three chajiters are devoted to the methods of mining 

 under the various conditions in the chief mines, the separation 

 of the diamonds from the kimberlite, of which they form from- 



* P. A. Wagner, "The Diamond Fields of South Africa.'' pp. xxv, 

 347, maps and illus. Johanncshuri; : T!ie Traiisz\ui! Leader. 1914. 



