OF WESTER2^ NORTH AMERICA, 



51 



slight indeed. Independent evolution both of the surviving archaic 

 and of the modern American lower Wasatch stock, with no evidence 

 of fresh Eurasiatic migrations. Establishment of certain character- 

 istically American families of mammals. 



Fig. 6.— Columnar section of the Bridger fonnation, Henrys Fork, western Wyoming. After studies 



by Matthew and Granger, 1902. 



Preliminary faunal divisions. — The Bridger has been separated 

 (Matthew, Granger) into four distinct faunal levels; A-D, marked 

 by distinct specific stages and generic stages, also by the appearance 

 and disappearance of certain types. 



1, Lower part of Bridger, levels A-B. Orvliippus zone. Char- 

 acterized by absence of Vintatherium; presence of Tiliodontia; 



