Samuel Franklin Emmons 



the expenditure of this energy might 

 be extended over a very long time, or 

 crowded into a comparatively short 

 one ; and his observations showed 

 him that at certain periods in geo- 

 logical history, the rate of change was 

 accelerated to such a degree that the 

 effect upon life produced was some- 

 what catastrophic in its nature. 



Of his great work upon systematic 

 geology, the larger part— that which 

 outlines the geological history of the 

 Cordilleran System — stands as firmly 

 to-day as it did when written, as 

 a correct and authoritative exposi- 

 tion. In view of the circumstances 

 under which the field-work was origi- 

 nally done, its essential correctness, 

 even in matters of minor detail, is 

 considered surprising by those who 

 have since had occasion to make de- 

 tailed studies of portions of the area 

 covered. 



In the more theoretical sections, 

 283 



