VI INTRODUCTION 



cable to human industry, and must take into account every influence, organic or 

 inorganic, which has had any bearing upon the life of the period or formation." 



Of all the definitions of geography which have been offered, the most 

 satisfactory is that it deals with the response of life to its environment. 

 The method of evolution is unknown, but the directive effect of environment 

 is unquestioned; by whatever method new forms arise the environment 

 largely determines the course they shall run and the ultimate fate of the 

 race. It is important, then, for this work that the term "environment" 

 and its contents be understood. To the author's mind environment may 

 best be denned as the sum of all the contacts which any organism or group 

 of organisms establishes with the forces, and matter of its surroundings, 

 either organic or inorganic. The results of this somewhat complex concept 

 of environment are discussed in the first chapter of the book. 



The author is well aware of the intricacy of the problem as here sug- 

 gested, but he is also most keenly aware of the inadequacy of attacking such 

 a problem from any more limited viewpoint. The efforts of the geologist 

 unacquainted with the principles of biology, or disinclined for any reason to 

 use them in his work, lead to imperfect and erroneous work; the converse 

 is just as true for the biologist. If the author shall succeed in impressing 

 the need for adequate training in both subjects and a careful consideration 

 of the problems from both sides, by all workers on paleogeography, an 

 important part of this work will have been accomplished. 



For the rest, any success which the author may have attained in picturing 

 the condition under which life developed during one of the critical periods 

 of the earlier history of the earth is largely due to the support which he has 

 received from the Carnegie Institution of Washington, and it is a pleasure 

 to record once more his sense of obligation to that Institution and its officers. 



E. C. CASE. 



