OF WESTERN NORTH AMERICA. 



55 



stages; the climax of separation between the North American and 

 western European faunae is reached at this stage. 



FAUNA." 



It is very important to note, as to the possible lower Oligocene age 

 of the Uinta formation {Diplacodon zone) : (1) That in the Bartonien 

 of France, which is reckoned as upper Eocene, but not the highest 

 stage, there appear the families Artiodactyla-Anthracotheriidse and 



Fic. S. — Columnar section of the Uinta formation, northern Utah. In A and B the diagram does not 

 properly represent the irregular nature of the so-called sandstones and clays, which are probably in 

 part coarser and finer volcanic-dust deposits. Modified from notes by O. A. Peterson, 1894. Fau- 

 nistic studies of Osborn. 



Perissodactyla-Chalicotheriidse; (2) that in the Ludien, which is reck- 

 oned as uppermost Eocene, or the highest stage, there appear the 

 families Marsupialia-Didelphyidse and Rodentia-Sciuridse; (3) that 

 none of these four families are known to occur in deposits older than 

 the lower Oligocene Plains formation of North America. We are there- 

 fore not justified, from our present knowledge, in transferring the Uinta 

 formation {Diplacodon zone) to the lower Oligocene, as some authors 

 (Scott) propose. 



a See Appendix, p. 91. 



