SOUTH DAKOTA SCHOOL OF MINES 



33 



The rock formations of the White River badlands repre- 

 sent a late time in geologic history. From the earliest days 

 of their exploration they have been recognized as of Tertiary 

 age and of non-marine character. The particular horizon 

 within the Tertiary to which the various subdivisions should 

 be referred have been less easy to determine. Leidy in his 



Figure 6 — Map of North America in the Tertiary period, Black areas 

 represent known exposures of marine Tertiary; lined areas, sea; 

 dotted areas, non marine formations. Scott. 



earliest studies of the extinct animals considered the beds 

 as Eocene. Fuller study indicated to him and others a 

 wider range in age than was first suspected and many fea- 

 tures showed a later Tertiary character. As a result they 

 became designated as Miocene and Pliocene, then as Lower 

 Miocene and Pliocene, the Miocene (or lower Miocene) be- 



