REVIEWS 431 



may be so obscured in older rocks as to be determinable only by the 

 closest observation. Hence, bedding, ripple marks, basal conglomer- 

 ates, and phenomena indicating unconformity afford material for 

 extended consideration. 



This review would be made too long by detailed references to the 

 second part of the "Principles," which treats of the historical geology 

 of the pre-Cambrian time. The discussion is arranged according to 

 districts and for each district the principle most saliently illustrated is 

 emphasized. This part of the book constitutes a valuable summary 

 of existing knowledge and a convenient and reliable reference. 



The style of the author is the expression of complete knowledge of 

 his subject, combined with exuberance of thought. Another great 

 writer, whose works are characterized by brilliancy and clearness, 

 recently said : "When I undertake to write a book I endeavor first to 

 see what I can exclude from it, and after the process of rigid exclusion 

 I carefully arrange the surviving ideas even to the order of paragraphs 

 before I write." The thoughts which rush upon Van Hise are related 

 in so many directions that many associations of the idea seek expres- 

 sion at once. His book would be easier to read and not necessarily 

 less accurate, if the thought were stripped. The logical analysis is 

 consistently carried out for all the major headings, but it is not ade- 

 quately extended to the paragraphs and sentences. Nevertheless, a 

 thorough study of the work leaves a profound impression of the 

 earnest purpose with which it has been conceived and of its value as a 

 contribution to one of the most difficult branches of geologic science. 



Bailey Willis. 



Topographic Atlas of the United States. Physiographic Types by 

 Henry Gannett. Washington : U. S. Geological Survey, 

 1898. 

 The enlightened policy adopted by our national Geological Sur- 

 vey of encouraging as wide a use as possible of the material gathered 

 at great expense receives a new and welcome illustration in the publica- 

 tion of the first folio of the above named series. It presents ten maps 

 as " illustrations of some of the simplest and most characteristic types 

 of topography to be found in those parts of the United States which 

 have been thus far mapped. Succeeding folios will illustrate more 

 complex forms." The origin of the atlas was in a proposition of the 



