860 THE JOURNAL OF GEOLOGY. 



tion of the various rock fades over the earth's surface is indicated. This 

 portion of the book which makes up the major part of Part III. (pp. 

 543-966) is largely systematic and classificatory in its nature and is 

 filled with a large array of facts and observations on the formation of 

 recent rocks and their distribution which cannot fail to be of great 

 value to the working geologist. Here again the author calls brief 

 attention to the alterations which the recent rock formations undergo 

 in becoming fossil the knowledge of which is essential to the under- 

 standing of fossil deposits. Two classes of such changes are distin- 

 guished, — metamorphism and diagenism. By metamorphism is under- 

 stood alterations caused by mountain pressure and volcanic warmth ; 

 and diagenism is defined (p. 693) as "all those physical and chem- 

 ical changes which occur in a rock after its deposition without the 

 action of mountain pressure and volcanic warmth." The book appro- 

 priately closes by outlining the possibilities of a comparative Mthology. 

 Throughout the book is urged the necessity of the historical geologist 

 giving equal prominence to the study of the conditions of formation 

 of the rocks and the conditions of growth of organisms. We make 

 prominent the study of the correlation of faunas in historical geology 

 and we should not neglect the study of the correlation of deposits. As 

 comparative anatomy based upon the correlation of organs is the most 

 important aid to palaeontologic work of reconstruction, comparative 

 lithology based upon the correlation of rock formations would prove a 

 valuable aid to the study of historical geology and the reconstruction 

 of earth history. 



In the chapters on equivalence of the rocks, correlation of facies 

 and changes in facies the author points the way to a scientific study of 

 comparative lithology and lithological correlation of sediments and 

 indicates some of the laws governing the deposit of sediments, which 

 complicated as they are, are important enough to be worthy of careful 

 investigation. 



On the whole the work is a thoughtful and carefully worked out 

 presentation of his theme, evincing long and careful work of observa- 

 tion and compilation and a just appreciation of the peculiar advan- 

 tages and the disadvantages of ontologic methods of research in histor- 

 ical geology. The two factors — the history of fossils and the history 

 of the rocks — are given equal prominence, and it is everywhere em- 

 phasized thctt the one cannot be studied successfully without the aid of 

 the other. E. C. Ouereau. 



