■5^'2 



NATURE 



[July 7, 1921: 



affected almost exclusively to the action of sul- 

 phuric acid produced by the oxidation of sulphur- 

 etted ores. This thesis is developed in detail 

 in a series of chapters devoted to the chemistry of 

 enrichment, in which the conditions of solution and 

 precipitation, so far as the more important metals 

 are concerned, are worked out in full detail. This 

 section is an admirable contribution to geo- 

 chemistry, and will well repay careful study. It 

 is perhaps possible that the author pins his faith 

 somewhat too exclusively to the action of sulphuric 

 acid and somewhat underrates the possible effect 

 of other solvents. In part this may be due to the 

 fact that he has confined his studies to the North 

 American continent and to the chemical changes 

 that characterise the temperate zones ; thus it is 

 significant that the word " lateritisation " is not 

 even once mentioned, and that this phenomenon, 

 which has played an important part in the 

 secondary modification of certain ore deposits in 

 tropical and sub-tropical regions, is here quite dis- 

 regarded. 



Each of the more important metals is then con- 

 sidered in detail ; the principal ores of each, their 

 solubilities and mode of occurrence, are discussed, 

 and the influence of enrichment is illustrated by 

 descriptions of a number of representative deposits 

 of each metal ; finally, the non-metallic or gangue 

 minerals are treated in the same way. It will be 

 obvious, even from this brief sketch, that the 

 author has done his work with great thoroughness, 

 and it is easy to foresee that this volume will 

 remain for a long time the standard text-book (for 

 such it really is) on the subject. 



It need scarcely be said that there are a number 

 of highly contentious points upon which it would 

 be hopeless to expect any general agreement 

 amongst geologists. Perhaps the phrase to which 

 most will take exception is a statement on p. 15 : 

 " Many of the rich deposits of gold are primary." 

 It is not too much to say that the exact opposite of 

 this will be more in accord with the experience of 

 most students of the subject, and that the state- 

 ment, ''None of the rich deposits of gold are 

 primary," would meet with far more general 

 acceptance. A gold deposit that has not under- 

 gone secondary enrichment is quite exceptional, 

 and many examples where such enrichment has 

 assumed a scale of great importance are familiar 

 to all economic geologists, e.g. the Witwatersrand 

 and in Western Australia. 



Far more difficult and more debatable is the 

 question whether the author has drawn rightly the 

 line of demarcation between the phenomena that 

 ought and those that ought not to be included in 

 the list of secondary enrichment. There are 

 NO. 2697, VOL. 107] 



numerous cases where material too poor to bee 

 economically workable (which the author, follow- 

 ing Ransome, designates as " protore ") has- 

 been enriched until it is worth working and thus; 

 becomes a true ore. Few will object to the in- 

 clusion amongst cases of secondary enrichment of 

 those protores that have been converted into ores 

 by the addition of valuable mineral matter, as, foir 

 example, the monzonite copper ores of Binghamv, 

 Utah, Ely, Nevada, etc. ; it is, however, far more; 

 doubtful whether the term can fairly be applied to- 

 deposits which have been enriched by the leaching 

 out or dissolving away of gangue material.. 

 Thus the important deposits of brown haema- 

 tite of Santander, Spain, have been derived^ 

 from ferriferous dolomite, containing only some- 

 3 per cent, of iron, by the solution of the carbon- 

 ates of lime and magnesia. It would probably be- 

 more correct to designate these as primary de*- 

 posits than to look upon them as enriched" 

 protore. Many writers classify them as^ 

 "residual deposits." Obviously, if Mr: 

 Emmons carried his method to its logical con- 

 clusion, he would include also clastic deposits,, 

 seeing that these are the result of the concentra- 

 tion or mechanical enrichment of mineral deposits; 

 that will in many cases have been protores. 



It is interesting to note that the author ha* 

 confined his attention to secondary enrichment, 

 and makes no specific reference to secondary im*- 

 poverishment as such ; necessarily he discusses the 

 phenomenon as antecedent to enrichment, but 

 there are certain cases in which the subject de- 

 serves attention for its own sake. 



Perhaps reference to such controversial points 

 as the above will serve better than anything else- 

 to bring out the diflficulties of the subject that Mr; 

 Emmons has so ably dealt with in this volume, 

 and both he and the United States Geological! 

 Survey are to be congratulated upon this impor- 

 tant contribution to the study of the phenomana* 

 of ore deposition. H. Louis. 



Our Bookshelf. 



The Elements of Theoretical and Descriptive- 

 Astronomy. By C. J. White. Eighth edition, 

 revised by P. P. Blackburn. Pp. xi4-309-f-ix 

 plates. (New York : John Wiley and Sons, 

 Inc.; London: Chapman and Hall, Ltd., 1920.) 

 175. 6d. net. 

 This book is something of a curiosity, if only 

 because it has reached an eighth edition. The 

 first edition was published in 1869 for the benefit 

 of the students of the U.S. Naval Academy. It 

 was an elementary primer giving the simple geo- 

 metrical facts of astronomy. So far as can be 



