Douglass : Merycochgerus. 91 



II. The Later Tertiary Formations oe the West. 



The geological position of these fossils is of as much interest, per- 

 haps, as their anatomical structure, and we cannot study the evolution 

 of the different forms without knowing the sequence of the different 

 horizons. I, therefore, take some space to discuss this matter. 



Dr. Matthew states th chxrus proprius is found " near the 



top of the White River formation (horizon C .*"" This seems in 

 harmony with Hayden's table in Leidy's " Extinct Mammalian 

 Fauna." yet I believe that to those who have not had time to look up 

 the matter with some care, there is apt to be a misunderstanding here, 

 and Dr. Matthew's use of the term " White River " may give a wrong 

 conception : nevertheless if one carefully reads the memoir, his mean- 

 ing is very plain. 



In 1862 Meek and Hayden 1S applied the names "White h 

 and "Loup River" (the latter overlying the former to two divisions 

 of the Tertiary in Nebraska and what is now South Dakota. 



The Loup R . were denned as folio 



"Fine loose sand, with some layers of sandstone, contains bones 

 of Canis, Felis, Castor, Equos, Mastodon, Testuco. etc., some of 

 which are scarcely distinguishable from living species. All fresh water 

 and land types." 



" On the Loup Fork of Platte River extending to an unknown dis- 

 tance beyond the Platte." 



Thickness 300 to 400 feet. Referred to Pliocene. 



The JJ7i 1 te River was denned as follows : 



■ • White and light drab clays, with some beds of sandstone, and 

 local layers of limestone. Fossils. Oreodon, Titanotherium, Ouvropot- 

 amus, Rhinoceros, Anchitherium, Hyanodon, Afacharodus, Tri, 



<do, Helix, Planorbis. Limnaa, Petrified wood, etc. All extinct. 

 No brackish water or marine remains 



"Bad lands of White River under Loup River Beds, on Niobrara 

 and across the country to the Platte 



Thickness 1,000 feet or more. Referred to Miocene. 



In 1877 Cope 1 * called Hayden's Santa Fe marls of New Mr 

 Loup Fork, and originated the term Loup Fork Epoch, which included 

 the Loup River beds of the Nebraska and Dakota region, bee- 

 similar age in Colorado, and the Santa Fe Marls. 



12 "Fossil Mammals from Colorado," p. 401. 

 13 /Vcv. Acaa. Xat. Sa\, Phila., Vol. XIII., pp. _ 



-SL Geol. Sua Vol. IV., part II., pp. 20, 361. 



