PREFACE 



THIS is an elementary textbook, not a manual or reference 

 book. The authors have sought to give the student (1) an 

 understanding of the general principles and processes of the 

 science, (2) a few of its fundamental facts, (3) an interest in 

 the subject, and especially (4) training in clear thinking. Many 

 of the mere facts of the science will be forgotten presently by 

 most students. The power and habit of reasoning logically 

 and of thinking clearly will be of service to the student in 

 meeting every problem of later life. The constant aim has 

 accordingly been to make the text explanatory rather than 

 merely descriptive, and to appeal to the judgment rather 

 than to the memory. The book has been written with the 

 belief that, while it is the duty of the teacher to develop in the 

 student the power to reason, it is the business equally of the 

 text. This has determined even the nature of the questions 

 asked at the ends of most of the Chapters, and elsewhere. 

 They are in general not questions the answers to which may be 

 found in the text, but questions which the student may reason 

 out for himself, provided the text has been read with under- 

 standing. 



The book departs from current practice more or less in the 

 arrangement of its material, and particularly in the omission 

 of separate chapters on volcanoes and earthquakes. Though 

 very interesting and from some standpoints important, vol- 

 canoes, and especially earthquakes, have been minor factors 

 in the development of the earth, so much so as not to merit, 

 in the opinion of the authors, the space commonly allotted to 

 them in textbooks. 



In the historical chapters "standard sections" have been 

 omitted because in general they are of relatively local appli- 



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