Revieivs — IVie Keoit Coalfield. 375 



since in proximity to a dyke the lode is always richer, while in the 

 absence of dykes the lodes are often barren. This relationship, 

 coupled with the fact that the dykes often carry sulphides in workable 

 amount, leads the author to the conclusion that the metalliferous 

 solutions were introduced along the dyke fissures. The unoxidized 

 sulphide ore consists for the most part of copper pyrites, mispickel 

 and iron pyrites either branching and intergrown or finely granular, 

 accompanied sometimes by tourmaline. An interesting variety, 

 found on the Chieftain mine, contains magnetite, both in the form 

 of round pellets and of threads intergrown with the copper pyrites. 



The lodes show a very well-marked division into the three zones 

 of oxidation, secondary enrichment, and sulphide ore. Since there 

 is no carbonate in the country rock, the salt produced was the soluble 

 sulphate, which was promptly carried down to the lower levels, 

 leaving the oxidized zone for the most part free from copper com- 

 pounds, except for the arsenate olivenite. This mineral, on one 

 claim, provided quite a large yield of ore, a fact which constitutes 

 somewhat of a curiosity in copper-mining. 



The zone of enrichment includes chiefly the minerals tile ore, 

 covellite, chalcocite, bornite, and copper pyrites ; it is of irregiilar 

 extent, but rarely exceeds a depth of 50 feet below ground water 

 level. In the unoxidized portions of the lodes the richer ores are 

 found in long narrow shoots, which may be several hundreds of feet 

 long,, but are only from 2 to 6 feet wide ; in addition to the shoots 

 the lodes contain large supplies of low-grade ore, which are now being 

 worked on account of the uncertainty and irregularity of the shoots. 



A fair amount of development work has been done on the field, 

 and a smelter has been erected and worked for several short periods. 

 The percentage of copper in the ores after hand-picking may rise as 

 high as twenty, but the more usuallevel is about seven. The great 

 difficulty, however, in mining at a profit is not the ore but the cost 

 of transport to and from Cairns, the nearest port, which is so high 

 as to make profitable working of the mines a very difficult Tuatter. 



"^ W. H. W. 



The Kent Coalfield : its Evolution and Development. By 

 A. E. Ritchie, pp. x + 309, with illustrations, maps, and 

 sections. Iron and Coal Trades Review, 1919. Price 7s. 6d. 

 rpHE world at large, and particularly the busier inhabitants of 

 -*- it, owe a great debt to compilers, and this debt is in no way 

 reduced by the issue of Mr. Ritchie's book on the Kent Coalfield. 

 The book is the result of the sifting of a vast mass of information, 

 geological, statistical, and financial, which must have been, to a very 

 considerable extent, in such inaccessible places as the files of the 

 daily j)apers and company reports. 



The author treats the subject historically, which is certainly the 

 most convenient way of placing before us the story which he tells, 

 but, as geologists, we could have wished that he had, at any rate. 



