460 



SCIENCE 



[N. S. Vol. LIII. No. 1376 



tive results are sought, but the difficulties of 

 obtaining them are recognized and the use- 

 fulness of quantitatively expressed results 

 that may not be accurate in themselves but 

 still may permit of valuable comparison with 

 one another, is admitted. The reader feels 

 throughout no impulse on the part of the 

 author to fix standards but merely that desire 

 to give help, out of his own rich but pain- 

 fully accumulated experience, which led him 

 to prepare the book. Any one who comes to 

 this book for a rigorous metliod that will 

 enable him to turn out orthodox studies of 

 sedimentary rocks will be disappointed, but 

 those who want to help in advancing the 

 borders of knowledge about this subject will 

 find guidance and inspiration. The methods 

 of analysis are grouped under tlu'ee heads — 

 physical, microchemical and clu-omatic. The 

 physical analysis includes different processes 

 sometimes grouped in this country under 

 mechanical analysis, and the preparation of 

 thin sections which in dealing with weakly 

 bound sedimentary rocks often calls for spe- 

 cial methods. The demonstration of tlie ease 

 of application and delicacy of microchemical 

 analyses is one of the outstanding features 

 of tlie book. Under chromatic analysis the 

 author discusses various methods of staining. 

 In the discussion of all these methods he 

 selects, weighs, evaluates and contributes on 

 the basis of his own experience, without at- 

 tempting any formal completeness. 



Perhap Cayeux's greatest achievement is 

 the interest he is able to give to liis dis- 

 cussion of the minerals of sedimentary rocks, 

 of which of course he considers only the more 

 common, both essential and accessory. It is 

 in this part of the book that his treatment of 

 the subject as natural history is illustrated 

 in the most novel and interesting way. The 

 individual mineral is to the author a record 

 of environments — of the environment in 

 which it originated and of those through 

 which it subsequently passed — and it there- 

 fore contributes to the reconstruction of the 

 history and geography of the past. 



The last part of the book deals with the 

 remains of organisms as constituents of the 



rocks. Needless to say, specific determina- 

 tions of organisms are not the purpose of a 

 treatise on petrography. But here, too, the 

 problem of past environment as recorded by 

 the remains, both as remnants of once living 

 organisms and as mineral substances, is the 

 object of study. This part therefore deserves 

 the attention of paleontologists as well as 

 of petrographers and stratigraphers. 



Vivified throughout by the author's own 

 experience the work must lack that perfect 

 completeness that would assure it against 

 being found defective in the treatment of 

 some special topics or methods that may be 

 in favor with individual readers. But every 

 reader will surely be glad to accept these 

 omissions for the sake of the vigor and 

 readibility that go with them. American 

 petrographers, for instance, will be struck by 

 the absence of any discussion of the use of 

 liquids of known indices of refraction in the 

 determination of minerals. But as compen- 

 sation they may profit by adopting some of 

 the elegant microchemical tests described, 

 which have the advantage that they can often 

 be applied directly to the thin section and do 

 not require the disintegration of the rock. 

 Likewise the suggestions given on pages 305 to 

 309 for the determination of minerals by 

 their general appearance may be a valuable 

 antidote to the habit into which the devotee 

 of " index liquids " is likely to fall, of resort- 

 ing to his liquids in blind routine, just as the 

 man with the slide rule habit gets out his 

 machine to find the product of 2X2. 



The physical quality of the book is worthy 

 of its subject matter, and it is a fact for con- 

 templation and an honor to the fine French 

 scientific spirit, exemplified by the entire 

 work, that it bears the date 1916. 



Marcus I. Goldman 



TJ. S. Geological Survey 



SPECIAL ARTICLES 



NOTES ON THE OCCURRENCE OF GAMMERUS 



LIMNAEUS SMITH IN A SALINE HABITAT 



The capacities of various organisms for 

 withstanding relatively wide ranges of environ- 

 mental conditions has received considerable 



