572 Reviews — The Gold Mines of the Rand. 



denudation of the Primary rocks. The metamorphic rocks of the 

 Transvaal consist chieflj' of altered igneous rocks, but the con- 

 glomerates are composed almost exclusively of quartz -pebbles, 

 without a single specimen of any other kind except sandstones. 



It seems certain that the age of the Witwatersrand beds will have 

 to be decided by mineralogical identity. Their relation to the 

 older rocks must not be considered as proved until some mineral 

 that is known to be peculiar to the metamorphic rocks is detected 

 in the matrix of the Banket beds. It is true that in the Zwarteberg 

 Mountains sandstones, with scattered quartz-pebbles similar to those 

 of the " Banket," are folded in with rocks in which Spirifers and 

 Terebratulge of Carboniferous species are said to occur. But it has 

 been demonstrated again and again how dangerous it is, in a folded 

 district, to argue the age of beds when closely associated or even in 

 actual contact. 



The classification of the auriferous conglomerates into a con- 

 formable and unconformable set has little geological importance. It 

 is impossible to correlate the conglomerates of outlying districts with 

 those near Johannesburg since there is really no distinctive litho- 

 logical difference between the various conglomerates. The paltry 

 difference in the size and number of the pebbles is no safe guide. 

 Even if there were a bed or group of beds that could with certainty 

 be recognized throughout the Southern Transvaal as occupying a 

 definite liorizon in the auriferous series, it would be extremely 

 difficult, owing to the faulted character of the country and the com- 

 plexity introduced by the intrusions of igneous masses, to piece 

 together the disjointed fragments that remain. 



The igneous rocks ai'e briefly described as basic " greenstones " — 

 diabase, epidiorite, and gabbro being recognized among others. 



No attempt is made to classify the faults and dykes according to 

 their relative ages. It is certain that many of the dykes were 

 formed prior to the deformation of the beds, since they have been 

 converted into schistose rocks, while others show no signs of altera- 

 tion. It is interesting, however, to find that reverse faulting is 

 recognized, which results in some cases in the reduplication of the 

 beds, as instanced on the property of the Witwatersrand Company, 

 where the conglomerates of the Main Beef Series have a double 

 outcrop. 



The origin of the gold is left an open question, but no connection 

 is found to exist between the gold contents of the conglomerates and 

 their pi'oximity to igneous masses or dykes. 



In the chapter on " Deep Levels " the authors have carefully 

 avoided introducing theory into their descriptions, and make no 

 allowance for the part played by reverse faults in bringing the 

 Main Reef Series nearer to the surface, but it is by no means an 

 impossibility that the members of the Main Eeef Series will be 

 found much nearer the surface than any ordinary flattening of the 

 beds could account for. 



From the facts brought forward by Messrs. Hatch and Chalmers 

 and other observers, it is certain that in the Kand formation the 



