230 Reviews — Faults and Dykes in Witivatersrand. 



borings and sinkings; and a Bibliography forms tlie concluding 

 portions of this memoir. 



The illustrations of ' llock-houses ' in Bunter Pebble-beds, and of 

 the ' Druid Stone ', a cemented mass of gravel at Blidworth, of the 

 quarries in Bunter for moulding-sand and in Keuper Marl for gypsum, 

 are interesting, but in our copy they are poorly printed. 



IV. — Faults and Dykes : A GEOLOfiiCAL Study of the Witwateesrand. 



]iy John S. Olvek. 8vo ; pp. vii, 298, with 62 text-illustrations 



and 6 plates. London: The Mining Magazine, Salisbury House ; 



Cape Town, J. C. Juta & Co., 191 1. Price 21.s. net. 



rilHIS is an expensive volume, judging from the amount of letter- 



JL press iind illustrative matter. These are well printed, but the 



figures and diagrams are not properly numbered and there is no index. 



The work, however, is one which has important practical applications 



in the gold-mining area of the Band, and should be of essential 



service to those engaged in the economic working of mines and in the 



development of fresh areas. 



The author commences in Part I with descriptions of faults, normal 

 and reversed, and of dykes which may be simple fissures or faults 

 filled with intrusive igneous matter. Various diagrams and calculations 

 are given with respect to fault-movements and slides or slide- thrusts, 

 and he observes that thrust movements on the whole are much greater 

 than the throws of ordinary faults. Attention is called to the 

 importance of observing all phenomena connected with displacements, 

 such as the presence or absence of drag ; the effects of tilting on 

 normal faults ; the character of the material with which the fissures 

 are filled, as a means of identification ; whether water-bearing and if 

 water ceases to flow from higher levels wlien tapped below ; and the 

 relative ages of tlie disturbances. It is observed that quartzites and 

 bankets are best examined when wet, dykes when dry ; that cleaved 

 quartzites are suggestive of the proximity of an important fault. The 

 character and composition of reefs, especially the size of pebbles, are 

 important in identifying particular bands. The author remarks that 

 "There appear to be a few well-attested cases on the Band in which 

 a dyke has been found to carry an appreciable amount of gold, and it 

 seems not at all improbable that such a dyke would enrich the reefs 

 in contact with it". He concludes, however, " that intrusive igneous 

 matter has played a very small part in the introduction of gold into 

 the banket." Finally, hints are given on mine-sampling. 



Part II contains a particular account of the geology of the Central 

 "Witwatersrand, illustrated by maps and sections. In his concluding 

 remarks the author states : "There appears, in fact, to be no basis 

 whatever for the traditional belief that the further course of the 

 Bietfontein Beefs must be towards the east. The only local evidence 

 of value points in a north-easterly direction. Whether the author's 

 theory with regard to a northern outcrop of the Main Beef Series is 

 sound or not can only be proved by actual boring operations, but it 

 can be confidently claimed that the balance of evidence at present 

 available is overwhelmingly in favour of the theory." While 



