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could be a large increment of heat as we approach the center. To 

 sum up the whole matter, his objections to the segregation of miscible 

 liquids are qualitatively correct, but the quantitative accuracy is 

 impaired by the nature of the assumptions on which the estimate is 

 based. These assumptions are thought to be incorrect in some 

 instances, and in all cases to lack the positive proof necessary for a 

 scientific demonstration. 



It seems unnecessary to assume that when immiscible liquids are 

 formed segregation can only take place along the walls, and therefore 

 involve extended molecular flow. 



Instead of this we conceive that the process may resemble crystalli- 

 zation and take place at many centers, and therefore involves 

 molecular flow through short distances. All stirring, currents, etc., 

 instead of hindering, would aid in this case. 



Finally, we have the fact of a regular rock gradiation established ; 

 a gradiation which is too widespread and uniform to be explained by 

 an original heterogeneity of earth, and a chance mixing of the lavas. 

 Our present knowledge, and the data at hand, are probably too meager 

 to exactly explain the processes by which such gradation was accom- 

 plished. Yet, we may not affirm, with Dr. Becker, that rock differen- 

 tiation is impossible under the known laws of physico-chemistry. 



The problem will doubtless yield when attacked by the methods of 

 modern physics and chemistry, and for this reason Dr. Becker's paper 

 is most timely. Cyrus Fisher Tolman, Jr. 



Afi Introductioji to Geology. By W. B. Scott. The Macmillan 

 Company. 1897. 573 PP- ;Si-90. 

 The preparation of a satisfactory text-book on any subject so large 

 as geology must always be a difficult matter. There is so much differ- 

 ence of opinion as to where emphasis should be laid, as to what should 

 be said and what omitted, and as to the order in which the topics should 

 be treated, that no book is likely to command universal approval in all 

 respects. Yet in spite of all the difficulties Professor Scott has suc- 

 ceeded in preparing a book which will command respect and probably 

 very general approval. He has shown in its preparation a sense of 

 proportion which the makers of text-books sometimes fail to exhibit. 

 When to this is added that he has made use of the newer literature 

 throughout, so that the book is up to date, it will readily be inferred 



