198 



NATURE 



[August i8, 1910 



after that the suction gas is much the cheaper. At 

 200 b.h.p. the suction gas is nearly one-third the 

 cheaper. 



Tliere are some very interesting folding plates show- 

 ing the pipe-work necessary for various designs of 

 gas-engines ; the various kinds of pipes — gas, water, 

 and exhaust — are shown in different colours, and thus 

 the matter is made very clear. 



Nearly ninety pages of the book are devoted to 

 descriptions of American gas-engines, made by West- 

 inghouse, Allis Chalmers, the Snow Engine, and many 

 others. Many of the drawings are dimensioned, and 

 the results of numerous tests are given. 



In part iv. various fuels available for producing gas 

 are described, and there is an extensive table on 

 American coals, giving for each full analysis and the 

 calorific value per pound; there is also information 

 with reference to blast-furnace gases and coke-oven 

 gas, also with regard to various oils, alcohol, &c. 

 There is an important table giving the explosive range 

 of various gases. The remainder of the book consists 

 of the theory of the gas-engine and producers, and in 

 the appendix the fullest particulars are given of the 

 methods of testing gas-engines prescribed by the 

 American Society of Mechanical Engineers and by the 

 German Societv of Engineers. This information is of 

 great importance, especially as at the present moment 

 there is nothing of the kind issued by any society of 

 British engineers in connection with gas- or internal- 

 combustion engines. 



STRUCTURE AND DISTRIBUTION OF ORE 



DEPOSITS. 

 Lchrc von den Erzlagerstatlen. By Dr. R. Beck. 



Dritte Auflage. Band i., pp. xii + 540+i map; 



Band ii., pp. x + 542. (Berlin : Gebriider Born- 



traeger, 1909.) Price, two vols., 32 marks. 

 TDROF. BECK'S "Lehre von den Erzlagerstiitten " 

 ^ is one of those works which disarm criticism. 

 The predominant feeling in the mind of the geologist 

 when using it must be of gratitude to its author for 

 this comprehensive and up-to-date account of the 

 structure and distribution of ore deposits. The pre- 

 vious edition was published in 1903, and an American 

 version, translated and edited by Weed, was issued in 

 1905. The new edition has been so much enlarged 

 that it now appears as two volumes, each almost 

 equal in size to the original. 



The book follows the same general lines as the pre- 

 vious editions, but there are many important changes 

 which indicate the trend of current opinion as to ore 

 classification. Prof. Beck divides ores into two primary 

 divisions, the epigenetic and syngenetic, those formed 

 respectively later and simultaneous with the rocks in 

 which they occur. These divisions are, however, prac- 

 tically abandoned in the work. The author divides 

 ores into eight groups, in which the first, seventh, and 

 eighth in order of treatment are mostly syngenetic; 

 the intermediate groups are epigenetic, but include 

 some ores which are admittedly syngenetic. The term 

 syngenetic, though it appears in the introduction, is 

 not much used, but epigenetic recurs frequentlv. That 

 NO. 2129, VOL. 84] 



term is not altogether satisfactory, as most of the 

 epigenetic ores are subterranean, and some of them 

 are very deep seated in origin. Hence epigenetic ores 

 are not epigene, but hypogene, to use two old and well- 

 established geological terms. 



The ores first treated are those attributed to direct 

 segregation in molten rocks. They are the truly 

 igneous ores. Prof. Beck recognises fourteen types, 

 of which all but four were included in the previous 

 edition. The only new type of oxide ores amongst 

 these is that of magnetite in granite, described by 

 Vogt, from the Lofoten Islands. Prof. Beck, however, 

 in a note added to the proofs, remarks that Sjogren's 

 recent paper confirms his own opinion that these 

 granitic ores are due to contact metamorphism, and 

 not segregation. The whole chapter on magmatic 

 segregation shows that less importance is attached 

 now than formerly to this process of ore formation. 

 The author includes the nickel ores of Sudbury in this 

 chapter, but recognises that they are mainly due to 

 secondary processes. He also quotes Loewinsen 

 Lessing's interesting work on the famous iron ores 

 of the Urals, which are thus shown to be contact 

 deposits and not segregations, as has been usually 

 maintained ; and as Prof. Beck points out, the great 

 Lapland ores, which have also been claimed as igneous 

 segregations, must be regarded as of the same origin 

 as those of tiie Urals. 



The group of ores which came second in the 

 previous edition, included those deposited by direct 

 sedimentation and precipitation. These aqueous ores 

 were placed next after the igneous, because both 

 groups are syngenetic. Description of the sedimentary 

 ores is now postponed till near the end of the book, 

 and the ores due to contact metamorphism take their 

 place. This significant change is a great improve- 

 ment, as many of the ores now assigned to igneous 

 segregation will probably be found to be contact 

 deposits. The bulk of the work is occupied with a 

 description of the epigenetic ores, which include 

 ordinary mineral veins and certain ores in stratified 

 rocks, due to the same process as ore veins. The 

 author includes here the banket of the Transvaal. He 

 gives an excellent judicial summary of the arguments 

 in favour of the rival theories as to the origin of that 

 ore without here expressing any very definite prefer- 

 ence. He obviously still favours the infiltration theory 

 which he has elsewhere supported. In reply to the 

 suggestion that much of the pyrites in the banket is 

 altered " black sand," he asks what has become of 

 the ilmenite that is usually associated with magnetite 

 in sucli deposits. There is, however, plenty of 

 titanic oxide in the banket which has probably been 

 derived from decomposed ilmenite. Little stress is laid 

 on the old arguments in support of the infiltration 

 theory, and according to Prof. Beck the weightiest 

 argument in its favour is the dependence of the gold 

 contents of the banket on its dip. This may be ques- 

 tioned as a matter of fact, and it is at any rate an 

 indefinite and unconvincing argument. The author 

 includes the West African banket as also epigenetic, 

 though he accepts its gold as alluvial in origin. It 

 is not surprising- to find this ore described immediately 



