256 REVIEWS 



Cotton is the success with which he appHes certain of Davis' principles 

 of physiography to the interpretation of New Zealand land forms. 

 His aims are well stated in the following sentence from the Preface: 



In the hope of setting forth these principles in a convincing manner and thus 

 popularizing in New Zealand the fascinating study of land forms, the present 

 work (Part i) is cast in the form of a textbook of geomorphology for New 

 Zealand students and general readers. 



In pursuance of this plan, the history of the science of geomorphology 

 is traced from its beginning early in the nineteenth century to the 

 present time. In this development, the work of American geologists 

 has been given a very important place. Following Davis, the distinction 

 is drawn between the empirical and explanatory methods of description 

 of land forms, and the great superiority of the explanatory method is 

 set forth. 



The central theme around which the subject-matter is arranged is 

 the concept of the erosion cycle. Several chapters are devoted to the 

 normal erosion cycle, and each stage is illustrated by New Zealand 

 examples, many of them from the author's own work. CompHcations 

 in the normal cycle claim a share of attention, as does also the arid cycle. 

 A comparatively recent extension of the principle of the erosion cycle 

 is its application to glacial action. As glaciation is a notable feature in 

 New Zealand, it naturally receives rather full treatment. Briefer 

 treatment is accorded to volcanoes and igneous activity, which are 

 considered as interruptions of the normal cycle. There is no lack of 

 igneous phenomena in New Zealand and some excellent illustrative 

 material is here incorporated. The closing chapters deal with the work 

 of waves and the development of coastal outlines. 



The organization of material is admirable. The numerous illustra- 

 tions are in most cases very effective, especially the line drawings. These, 

 together with the writer's lucid and interesting style, make the book 

 very attractive. It should make a valuable addition to any geological 

 library and merits considerable attention from students of physiography 

 in countries other than the one about which it is written. 



A. H. B. 



Silver Enrichment in the San Juan Mountains, Colorado. By 

 Edson S. Bastin. Bulletin 735-D, United States Geological 

 Survey, Washington, D.C., 1922. Pp. 67, figs. 18. 

 The paper presents primarily some details of silver enrichment in 



the San Juan Mountains as shown by a study of polished ore specimens. 



It was not possible for the writer himself to consider exhaustively the 



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