24 



The Bad land Formations of. the Black Hills Region 



The badland formations of the Black Hills region,, from 

 the earliest days of their exploration, have been recognized as 

 of Tertiary age and of non-marine character. Their relation to 

 the marine and non-marine deposits throughout the North 

 American continent is shown in Figure 4 from Scott's Intro- 

 duction to Geology, 1907. 



Figure 4 — Map of North America in the Tertiary period. Black areas — 

 known exposures of marine Tertiary; white areas — land; lined areas — 

 sea; dotted areas — non-marine formations. After Scott. 



The particular horizon within the Tertiary to which the 

 various subdivisions should be referred has been less easy to 

 determine. Leidy in his 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 

 features showed a later Tertiary character. As a result they be- 

 came designated as Miocene and Pliocene, then as Lower Mio- 



