March 28, 1901] 



NA TURE 



511 



secondary phenomenon, and Dr. Beck is most probably 

 in error when he ranks this among the primary modifica- 

 tions of ore deposits. The description of secondary 

 alterations of deposits and the formation of gossans is 

 extremely good, the chemical investigation of the subject 

 being especially convincing. It must be noted that Dr. 

 Beck only refers under this head to secondary changes 

 above the permanent water-level (in the region of 

 Posepny's vadose circulation) and not to the phenomena 

 which have recently attracted so much attention in 

 America, and which, under the head of Secondary 

 Enrichment of Ore Deposits, have been so ably investi- 

 gated by Emmons, Weed and others ; these Dr. Beck 

 appears to omit entirely. 



The section on the alteration of the wall rocks of 

 mineral veins either by the influence of these veins them- 

 selves or by the agencies that have played an importajiit 

 part in the deposition of the mineral constituents of these 

 veins, is a valuable summary of a very important subject, 

 which has only in comparatively recent years attracted 

 the attention that it deserves. 



Coming next to the classification of other mineral de- 

 posits, or as Dr. Beck rather awkwardly designates 

 them, " Not vein-like epigenetic ore deposits within 

 stratified rocks," the subdivision is far from satisfactory. 

 They are divided, first of all, as follows : — 



A. Epigenetic ore beds. 



B. Epigenetic ore masses. 



C. Contact-metamorphic ore deposits. 



D. Ore-bearing fillings of cavities. 

 Unfortunately, the first group contains many deposits 



that are generally looked upon as typical masses, e.g. 

 the lenticular masses of cupriferous pyrites of the Huelva 

 region. The group is subdivided into deposits occurring 

 in crystalline strata and deposits in non-crystalline strata 

 formed by impregnation, each class being then again sub- 

 divided according to its mineral contents. This classifica- 

 tion is unfortunate, as it causes the author to describe the 

 above-mentioned pyrites deposits as produced by im- 

 pregnation ; it would hardly be possible to assign a less 

 probable genesis to such deposits as these, consisting 

 as they do mainly of dense massive pyrites practically 

 free from gangue, and it seems impossible to imagine 

 that any one who has ever studied these deposits can 

 seriously believe that they owed their origin to impreg- 

 nation. It is in any case most unlikely that a system 

 of classification that forces these deposits and the Nor- 

 wegian and other similar pyrites deposits into different 

 groups, and that takes, moreover, no account of the 

 eruptive rocks with v/hich they are so closely associated, 

 can possibly be correct. 



The group of Epigenetic ore masses is a rather more 

 coherent one than its title implies, Dr. Beck confining 

 this group to irregular deposits in calcareous rocks. It is 

 perhaps doubtful whether this is the right place for those 

 very puzzling deposits that are generally spoken of as the 

 gold-bearing " reefs " of Pilgrim's Rest, Lydenburg ; it 

 is perhaps more likely that these will prove ultimately 

 to be true bedded deposits, though their real character 

 is to-day far from clear. 



The next division of the book contains a short but 

 good description of alluvial deposits ; the objections to 

 the independent treatment of this group of deposits 

 NO. 1639, VOL. 63] 



have already been pointed out. Apart from these, Dr. 

 Beck's descriptions are thoroughly satisfactory. 



The work concludes with a brief but good chapter of 

 general hints upon the search for mineral deposits. In 

 this the author attempts, and with considerable success, 

 to show that the scientific study of mineral deposits can 

 give information of the greatest value to prospectors, 

 and that his subject accordingly possesses, not merely a 

 scientific and academic, but also a technical and com- 

 mercial interest that should not be overlooked. This 

 last chapter may more especially be recommended to 

 the large number of mining engineers in this country 

 who appear to think that the study of mineral deposits 

 is one that they can venture to neglect as of no practical 

 importance. 



It is satisfactory to find that the wish expressed in 

 the review of the first part of this book has been gratified, 

 and that it is furnished with a good topographical as 

 well as a general index, and it is a pleasure to be able 

 to congratulate Dr. Beck on the production of a work 

 of standard value upon the fascinating subject that he 

 has done so much to advance. Henry Louis. 



ORGANIC CHEMISTRY. 

 Practical Organic Chemistry for Advanced Students. 

 By Dr. Julius B. Cohen. Pp. xi ■\- 284. (London ; 

 Macmillan and Co., Ltd., 1900.) Price is. 6d. 



IN this enlarged edition Dr. Julius Cohen has increased 

 greatly the value of the book as a manual for 

 advanced students by adding chapters on organic 

 analysis and the determination of the molecular weight. 

 Under the latter heading we are glad to see he describes 

 the preparation of the silver salts of organic acids and 

 of the platinum salts of bases — two operations the de- 

 scription of which is frequently omitted from similar 

 works. The appendix, which treats of the theory in the 

 form of a note on each preparation, has also been 

 enlarged. Our experience has been that students will 

 not trouble to hunt theory in the limbo of an appendix, 

 and the matter of these notes would have been more 

 usefully incorporated in the preparations themselves. 

 The explanations are necessarily condensed and fre- 

 quently difficult to understand ; for example (p. 193), 

 " Aldehydes can only be obtained directly from the fatty 

 acids by distilling the calcium salt with calcium formate ; 

 but in no case by direct reduction, unless in the form of 

 lactones.^' 



The preparations are well and clearly described, and 

 the apparently obvious is not ignored. Thus we read 

 (p. 43), " A small balance with celluloid pans, for use 

 on the bench, is indispensable." Such a balance is 

 invariably used by German students in order to estimate 

 their yields, but is a sufficiently rare object in an English 

 laboratory. 



Details of the preparation of ninety-seven substances 

 are given, and consequently the book will be of great 

 service, not only to the student, but also to the lecturer. 

 Of the fifty-six substances usually prepared by the honour 

 students at the Owens College, fifty-two are to be found 

 in this book. 



In a useful series of " Hints on the investigation of 



