42 ENVIRONMENT OF VERTEBRATE LIFE, ETC. 



A monotonous environment is one where there is little change in the 

 factors, static or dynamic, which form the group of contacts and into which 

 no new elements are introduced and none are abstracted. Such an environ- 

 ment permits close adjustment of forms, but tends toward the perpetuation 

 of archaic forms. The environment may be at the same time complex, 

 relatively, and monotonous. In such a case there may be an accumulation 

 of stresses which would cause rapid expansion and evolution of life when 

 the status was disturbed. The depths of the sea, a desert, or a great plain 

 would approximate this condition. 



A diversified environment contains many shifting factors which con- 

 tinually introduce new elements into the problem, facilitating or inducing 

 rapid and radical changes. A region undergoing climatic change, inunda- 

 tion by the sea, or elevation resulting in greater aridity, the spread or retreat 

 of vegetation, etc., are illustrations. 



With this very brief statement of the very comprehensive conception 

 of the environment, it is obvious that almost every force or kind of matter 

 must be reckoned with as a possible agent in the development of any group 

 of organisms. Because of this complexity and the necessity for the con- 

 sideration of combinations of factors, especially in the study of extinct 

 forms of life, usually treated separately and only by specialists in widely 

 divergent fields, it is obvious that the environment is the dominant element 

 in any paleogeographic problem. 



VIII. CHECKS ON THE GEOLOGIST. 



It is obvious from the above that the solution of a paleogeographic prob- 

 lem involves far more than the discernment of the boundaries of deposits or 

 the mapping of the occurrences of peculiar forms of life. Nor can the pecul- 

 iarities of a fauna or flora be explained by the relation of the individuals of 

 the biota to the inorganic environments alone. 



The geologist who would restore the condition of the earth at any definite 

 interval of time may not limit himself to the interaction and results of 

 inorganic forces, for his restoration would be incomplete and far from 

 accurate. Even if he designedly deals with such forces alone and desires to 

 present only the incomplete picture, he is helpless to delimit the land and 

 water areas without using indices supplied by the response of organic things. 

 He is not entirely justified in his criticism of the biologist who would raise 

 a continent to transfer a toad from one side of the sea to another, for after 

 all the things are there and their presence must be explained, though the 

 biologist may have been too enthusiastic in his epeirogenic efforts and too 

 ready to refer the distribution to geological agencies. 



The geologist may be far wrong in his interpretations of structures 

 unless his knowledge of life is ample. The author again calls to notice 

 his experience on an area of wind-blown sand in a desert portion of Arizona, 



