396 H. S. WILLIAMS CORRELATION PROBLEMS 



Evolution hypothesis. — The other hypothesis, the evolution hypothesis, 

 rests on two almost diametrically opposite propositions. 



I. The first of which is that a species subjected to unfavorable condi- 

 tions of environment adjusts its morphologic characters, and that the 

 differences observed in the faunal composition between a given fauna and 

 the fauna stratigraphically underlying it is the result of modification of 

 those species capable of making the adjustment and the killing off of 

 those not capable of adjustment. 



II. The second proposition is that the second fauna is really a newly 

 evolved fauna, not contemporaneous with the first, but actually repre- 

 sents a later period of time wherever it is found. 



This evolution hypothesis also appears to be founded on well known 

 facts of geographical distribution and what we know of the effects pro- 

 duced on living species by abnormal conditions of environment to which 

 they are exposed. 



This second set of problems, like the first, is familiar to us all ; but are 

 we aware of their great significance in reaching right interpretation of 

 our fossils? Are we not unscientific in supposing that our hypotheses, 

 our assumptions, our fundamental ideas, our modes of reasoning, will 

 take care of themselves if only we accurately record our observed facts? 



The problems to which I have referred confront us all when we at- 

 tempt to interpret fossils. It is easy to state what they are, but their 

 solution will require serious consideration if we are to make real progress 

 in our science. 



Conclusions 



In conclusion, I will state that after a study of the facts available I 

 feel a reasonable confidence in correlating the fauna of the Edmunds 

 formation with the fauna of the Wenlock limestone and shale of Eng- 

 land. But the facts do not seem to me to warrant the statement that 

 the Edmunds formation and the Wenlock are contemporaneous in any 

 such sense as to enable us to draw definite geographic boundaries of some 

 particular epoch of geologic time. 



The problems to which I have called attention do not involve uncer- 

 tainties regarding the morphologic characters of fossils, but uncertain- 

 ties regarding the modes of thought and reasoning, the controlling ideas, 

 by which we interpret fossils into terms of time-relations and paleoge- 

 ography. 



Considering the importance of having right premises even in scientific 





