PREFACE. 



Iu the preparation of these essays I have had several objects in 

 view, among which are a further presentation of elementary matter 

 pertaining' to biological geology than has before been published, the 

 defense of biology as an indispensable aid in geological investigation 

 and the repudiation of certain untenable claims that have been made 

 in its favor, an application of the principles discussed to the practical 

 work of the geologist, and the demonstration of the necessity of the 

 preservation of fossil remains in public museums as storehouses of 

 evidence upon geological questions. These essays are therefore con- 

 lined mainly to a discussion of questions pertaining to biological 

 geology, including both its structural and systematic branches, only 

 incidental reference being made to other important branches of geo- 

 logical science, such as mineralogy, lithology, dynamic geology, etc. 



I have intended an approximately full statement of the subjects 

 selected for discussion as well as scientific accuracy in my conclusions, 

 but in the manner of their presentation I have chosen to address gen- 

 eral readers and students of geology as well as special investigators. 

 I have accordingly presented a more detailed and methodical state- 

 ment of the principal facts upon which biological geology is based 

 than otherwise would have been thought desirable. Every working 

 geologist is necessarily more or less familiar with the principles and 

 criteria which are based upon these facts, but a comprehensive knowl- 

 edge of them is not yet accessible to the student except by personal 

 experience or didactic instruction; that is, because these principles 

 and criteria have not yet been systematically and fully stated in pub- 

 lished works the greater part of accessible knowledge concerning them 

 is traditional. 



It is true that some of the knowledge referred to has been briefly 

 and more or less clearly presented in text-books, but the elements of 

 biological geology are too comprehensive to allow of a satisfactory 

 summary in even the largest of them. All discussions of principles 

 and criteria pertaining to that subject are also usually omitted by 

 authors of other works, evidently upon the reasonable ground that 

 scientific writings ought not to be encumbered by a repetition of ele- 

 mentary principles, and upon the less reasonable assumption that the 



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