PREFACE 



It is the author's hope that this book may find a place as a 

 class-book dealing with the historical geology portion of a one-year 

 course in general geology, and that it may also serve as a text for 

 special courses in historical geology. An elementary knowledge 

 of what is generally comprised under dynamical and structural 

 geology is presupposed. It is assumed that a proper amount of 

 laboratory and field work will be pursued in connection with the 

 text. 



It will be seen that more introductory space is devoted to a dis- 

 cussion of the broad fundamental principles of historical geology 

 than is customary in text-books. The experience of the author 

 has been that careful attention to these general principles at the 

 beginning of the subject is well repaid in satisfaction to both teacher 

 and student when the great events of earth history are taken up in 

 regular order. 



A definite plan is strictly adhered to in the discussion of each 

 period from the Cambrian to the Tertiary inclusive. Such defi- 

 niteness of presentation, in spite of some objections which may be 

 raised against it, should greatly aid the beginner, who must con- 

 stantly compare periods and note the important changes in the 

 evolution of both land-masses and organisms. The topical arrange- 

 ments are such that any desired comparisons can be readily 

 made. A plan of treatment, the same for both the Archeozoic 

 and Proterozoic eras, permits a ready comparison of these two. 

 By the very nature of the subject-matter, a somewhat more special 

 method of discussion has been necessary for the Quaternary period. 



Important features are the summaries of Paleozoic and Meso- 

 zoic history which will aid the student in fixing in mind the salient 

 points in the history of those two great eras. It is believed that 

 the two tabular summaries — one of Paleozoic life and the other 

 of Mesozoic life — will be helpful. Group by group and period 

 by period, from the Cambrian to the Cretaceous inclusive, the 

 principal evolutionary changes in organisms are brought before 

 the student at a glance by the use of these tables. 



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