Fbbruabt 11, 1887.] 



SCIENCE. 



143 



not have acted at different times, — one that car- 

 ries with it the fallacious conclusion that the 

 lithological character of a rock is any reliable in- 

 dication of its geological age. 



Chapter viii., entitled ' A natural system in 

 mineralogy,' suggests a new basis of mineralogi- 

 cal classification, and illustrates it in a new classi- 

 fication of the silicates. These are divided into 

 three main groups, according as their bases are in 

 the protoxide state (protosilicates), in both the 

 protoxide and sesquioxide states (protopersllicates), 

 or wholly in the sesquioxide state (persilicates). 

 These groups are further divided into various 

 tribes according to principles which cannot be 

 explained in this place. Whatever may be the 

 chemical merits of this system, it would appear to 

 do serious violence to the cry stall ographic rela- 

 tionships of certain minerals, as may be seen in the 

 wide separation of the members of the pyroxene 

 and amphibole groups. 



The three remaining essays are of an historical 

 character, and contain a vast amount of informa- 

 tion regarding the views which have been held on 

 the subject of crystalline rocks. The first of these 

 is a summary of the writer's report E of the 

 Second geological survey of Pennsylvania, on the 

 pre-Cambrian rocks in America and Europe. The 

 second deals with the geological history of the 

 serpentines, and develops the writer's idea that 

 all serpentines are of aqueous origin, being of the 

 nature of chemical precipitates. The chemical 

 origin of a small and long-since buried bed of a 

 serpentine- like deposit occurring in the Onondaga 

 salt-group at Syracuse, N.Y., and of the magne- 

 sian silicates (sepiolites) of the Paris basin, to- 

 gether with certain reactions which are found to 

 take place between the carbonates of lime and 

 magnesia and free silica in heated solutions, are 

 adduced as a proof that all serpentine is of chemi- 

 cal origin. There seems here to be a very partial 

 and one-sided statement of the best authorities on 

 this subject, for the origin of serpentine by the 

 hydration of eruptive chrysolitic rocks will surely 

 be disputed to-day by no one who has carefully 

 and impartially looked into the matter. Though 

 there may be truth in both hypotheses, there is 

 more evidence in favor of the latter ; so that here, 

 again, the danger of accounting for all rocks of 

 similar character by one set of causes becomes 

 apparent. 



The final essay is devoted to an elaborate review 

 of the Taconic question and a statement of the 

 writer's opinion that the Taconic of Emmons is a 

 formation of the transition class, which uncon- 

 formably underlies the Cambrian, and is separated 

 from it by a great interval of time which includes 

 the Keweenian period. 



Throughout, the book is interesting, — almost 

 fascinating, — but nevertheless full of danger to 

 any one who accepts it implicitly as a guide, or 

 to the beginner who is not able to estimate it in 

 comparison with the work of others. 



REMSEN'S ELEMENTS OF CHEMISTRY. 



In the preface to his ' Elements of chemistry,' 

 Professor Remsen states his opinion, that if a 

 course in chemistry " does not to some ex- 

 tent help the pupil to think as well as to see, to 

 reason as well as to observe, it does not deserve 

 to be called rational." An essential part of his 

 plan in this elementary course is the performance 

 of experiments by the pupil, who is then to be 

 questioned by the teacher concerning the results of 

 the experiments, and the conclusions to be drawn 

 from them. Appropriate questions are given in 

 the book in connection with the description of 

 each experiment, and a quite extensive list of 

 questions and problems (not numerical) is append- 

 ed at the end of the work. A number of experi- 

 ments, with questions, illustrative of chemical 

 change in general, are given at the outset, before 

 even the names of the elements, or the distinction 

 between elements and compounds, is imparted. 

 The atomic theory and that of valence are treated 

 briefly and clearly, special care being taken to 

 prevent the too common confusion of facts and 

 hypotheses in the young student's mind. A great 

 deal of attention is devoted to subjects which 

 are likely to interest the pupil by reason of their 

 practical importance or their relation to his daily 

 life. Such are the manufacture of soap and 

 paper, fermentation, bread-making, the working 

 of iron, and the impurities of water. In these as 

 well as in other subjects the endeavor seems to 

 have been made to introduce all of the most re- 

 cent discoveries and advances which are suitable 

 to an elementary treatise. Examples are the 

 water-gas process, the liquefaction of the 'per- 

 manent' gases, the electrical furnace, celluloid, 

 cocaine, and artificial alizarin. 



About one-ninth of the volume is devoted to a 

 description of some of the compounds of carbon. 

 The relations between the principal classes of 

 these bodies are pointed out, but no attempt is 

 made to teach the structural formulae of the 

 more complex compounds. 



The U.S. consul at Palermo, Mr. Philip Car- 

 roll, has forwarded to the state department a 

 translation of a pamphlet issued by Prof. E. 

 Albanese, president of the sanitary council of 



The elements of chemistry. By IBA Eemsen. New York, 

 Holt. 12°. 



