NA TURE 



583 



THURSDAY, JANUARY 28, 1915. 



! TREATISE ON USEFUL MINERALS AND 



ROCKS. 

 The Deposits of the Useful Minerals and Rocks, 

 their Origin, Form, and Content. By Prof. 

 Dr. F. Beyschlag, Prof. J. H. L. \'ogrt, Prof. 

 D. P. Krusch. Translated by S. J. Truscott. 

 \'ol. i. Pp. xxviii + 514. (London: Macmillan 

 and Co., Ltd., 1914.) Price 185. net. 



THIS book is the Eng^lish version of the first 

 volume of a comprehensive treatise on 

 useful minerals and rocks by three authors who 

 are collectively well qualified to .deal with the sub- 

 ject, both from the scientific and the economic 

 points of view. The work, when complete, will 

 consist of three volumes, two of which, dealing- 

 with ore-deposits, have already appeared in Ger- 

 man. Its main object is to explain and illustrate 

 by descriptions of individual occurrences the 

 g^eneral principles g-overning- the nature and mode 

 of occurrence of the deposits. The authors em- 

 phasise the fact, now generally recog^nised, that 

 a knowledgfe of the causes which have resulted in 

 the formation and deformation of these deposits 

 is of value to all persons who are eng-ag^ed in 

 exploiting- the mineral resources of the world. 

 Their point of view is thoroug-hly scientific, and 

 the classification which they adopt is, therefore, 

 primarily based on g^enetic principles. 



Ore deposits are divided into two g-reat g-roups, 

 to which the terms syng-enetic and epigenetic 

 are applied ; those of the former orig-inate at the 

 same time as the country rock, those of the latter 

 have been broug-ht into the positions which they 

 now occupy after the country rock had been pro- 

 duced. The syng-enetic group includes mag-matic 

 seg-reg^ations and sedimentary deposits. The epi- 

 genetic g-roup includes contact-deposits, cavity 

 filling's (including- lodes) metasomatic deposits, 

 and impregnations. 



Having sketched in broad outline their scheme 

 of classification, the authors deal with the causes 

 which have determined the forms of the different 

 deposits, describing- in this connection the g-eneral 

 principles of folding-, faulting, over-thrustingf, and 

 the like. Then follow chapters on the minerals 

 found in ore-deposits, on the various modes of 

 formation of these minerals, on the relative dis- 

 tribution of the elements, with special reference 

 to the metals, and on the orig-in of ore -deposits. 

 The main causes to which the g-enesis of ore- 

 deposits is attributed are crystallisation from 

 molten magmas, pneumatolysis, contact-meta- 

 morphism, metasomatosis, precipitation from 

 solution, and the mechanical concentration of pre- 

 NO. 2361, VOL. 94] 



existing minerals. In dealing with the origin of 

 ore-deposits by crystallisation or precipitation 

 from solution, they practically discard the old, and 

 atone time popular, theory of "lateral secretion," 

 and accept the view that, if we leave out of 

 account the effects of surface action on ore- 

 deposits already formed, the solutions came from 

 below and can in most cases be connected either 

 directly or indirectly with igneous action. 



Having dealt with general principles and given 

 I a historical sketch of the classifications adopted 

 by different writers from the time of Werner to 

 the present day, the authors proceed to consider 

 the different types of deposit under four heads : 

 (i) magmatic segregations, (2) contact deposits, 

 (3) lodes, irregular cavity fillings, and metasomatic 

 deposits, and (4) ore-beds. About half of the 

 volume under review and the whole of the second 

 volume, which has not yet appeared in English, 

 is devoted to the description of typical occurrences. 

 The first two of the above groups are dealt with 

 in this book together with tin-lodes and quicksilver 

 deposits which belong to the third group. As an 

 illustration of the method of treatment adopted 

 in this portion of the work we may very briefly 

 summarise the account given of the nickel- 

 pyrrhotite group of sulphide ores. These deposits 

 form a widely-distributed and well-marked group. 

 The most important characteristic common to 

 them all is that they occur within, or at the 

 margins of, masses of norite or gabbro. Thus 

 of fifty occurrences in Norway by far the greater 

 number occur in unaltered norite. The most im- 

 portant minerals are nickeliferous pyrrhotite, 

 pyrite, and chalcopyrite. The pyrrhotite usually 

 contains about 2*5 per cent, of nickel with some 

 cobalt. Sometimes the proportion rises to 8 or 

 even 12 per cent., but in such cases the presence 

 of pentlandite, (FeNi)S, can be easily recognised 

 and, owing to recent researches on metallographic 

 lines, it may be regarded as certain that the ab- 

 normal percentages of nickel present in certain 

 cases are due to admixed pentlandite ; whether, in 

 addition, a smaller nickel and cobalt content enters 

 into the composition of pyrrhotite still remains 

 an open question. 



As regards the morphology of the deposits, the 

 authors point out that transitions occur from 

 normal gabbro or norite containing less than i f>er 

 cent, of sulphides to rocks containing 10 or even 

 30 per cent. Such varieties are termed pyrrhotite- 

 norite, and from these to masses of practically 

 clean sulphides transitions may also be found. 

 From these and many other facts, the authors 

 conclude that the nickel-pyrrhotite def>osits are 

 the result of segregation from a basic magma. 

 Having thus dealt with generalities, they proceed 



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