276 G. B. RICHARDSON THE MONUMENT CREEK GROUP 



of knowledge can not be made. And in this connection it should be em- 

 phasized that, notwithstanding the detailed work that has been done, 

 exact correlations of riiany of the early Tertiary formations are not yet 

 possible. A large number of stratigraphic sections and fossil collections 

 prove that the early Tertiary history of the region was complex. There 

 is evidence of local uplift in different areas at different times, and the 

 consequent varied topographic conditions gave rise to diverse, isolated, 

 continental deposits. Moreover, changing environment must have had 

 its effect on animal and vegetable life, so that the varied conditions ex- 

 isting at the same time in different parts of the region may have made 

 it possible for different forms of life to exist simultaneously in different 

 •areas. These factors complicate the task of correlation and in a measure 

 account for the slow progress that is being made in solving early Tertiary 

 stratigraphic problems in the Rocky Mountain region. 



