676 THE JOURNAL OF GEOLOGY. 



70,000,000 years as a maximum for post-Archean Geologic time. 

 I have not referred to the rate of development of life, as that is 

 virtually controlled by conditions of environment. 



In conclusion, geologic time is of great but not of indefinite 

 duration. I believe that it can be measured by tens of millions, 

 but not by single millions or hundreds of millions of years. 



Charles D. Walcott. 



