X PREFACE 



and dogmas, and renders further progress exceedingly difficult to 

 him. In no science are there more open questions than in Geol- 

 ogy, in none are changes of view more frequent, and in none, 

 consequently, is it more important to emphasize the distinction 

 between fact and inference, between observation and hypothesis. 

 An open-minded hospitality for new facts is essential to intel- 

 lectual advance. 



The order in which the different sections of the book are taken 

 up should depend somewhat upon the season of the year in which 

 the study is begun. The chapter on the Rock-forming Minerals is 

 intended rather for reference than for actual learning, and should 

 at first be employed only to give the beginner a notion of what 

 minerals- are like and to familiarize him with a few of the com- 

 monest and most important kinds. The unfortunate likeness in 

 the terminations of the names of so many minerals and rocks is a 

 source of great confusion to the beginner. It is, therefore, impor- 

 tant that he should have grasped the conception of what a mineral 

 is, before commencing to deal with rocks. A repeated experience 

 of this confusion has led to the wide separation of the chapter 

 upon minerals from those treating of the rocks. It is perhaps 

 hardly necessary to say that a knowledge of elementary inorganic 

 Chemistry is indispensable to an understanding of almost any part 

 of Geology, and especially of those parts which are concerned with 

 the minerals and rocks. 



If the course of study be commenced in the autumn, it will be 

 well to take up first the chapters upon the Surface Agencies, or 

 even the Structural Part, according to the opportunity for out- 

 door work and occasional excursions. When it is possible to 

 undertake it, this work in the field should by no means be 

 omitted. Even for those who have no intention of becoming 

 geologists, observation at first hand possesses a far higher interest 

 and charm and a much greater educational value than merely 

 reading books or hearing lectures. Such observation is also a 

 corrective of the false impressions which are necessarily given by 

 the somewhat artificial and systematic treatment of a vast subject 

 in a text-book. In many cases, it is impracticable for the teacher 



