62 



CEXOZOIC MAMMAL HOKIZONS 



MIDDLE OLIGOCEXE (EUROPE. ETAGE ST.\:^1PIEX [TOXGRIEX 



SUPERIEUR]). 



9. LOWER PART OF BRULE CLAY (DARTON : OREODON ZONE AND 'METAMY- 

 NODON SANDSTONES." 



(Figs. 1, 9, 10; Pb. I-III.) 

 HOMOTAXIS AXD SYXOXYMT. 



North America. — 1. Horizons B and C of Hayden and Leidy. 2, 

 Oreodon zone of Leidy. 3, Lower Brule clay of Dart on." 4, " JHeta- 

 mynodon sandstones" of Wortman.^ (1-4 all of South Dakota.) 5, 

 'Tedar Creek beds'" of Matthew.^ northeastern Colorado. 6, "Wide- 

 spread similar exposures in southeastern Wyoming, South Dakota, 

 and northwestern Nebraska. 7, Scattered exposures in western 

 Montana. 



Europe. — Approximate homotaxis ^-ith the Stampien or Ohgocene 

 moyen of Europe is indicated b}' similar stages in the evolution 

 of Artiodactyla-Anthracotheriidae {Hyopotamus) , of Perissodactyla- 



Amynodontid^e (e. g., Metamy- 

 n odon , Cad urcotTieri u m ) , of Tapi- 

 rida^, of Rliinocerotida?, and of 

 Chalicotheriid^e. Also by the 

 apparent disappearance in both 

 countries of Perissodactyla- 

 Amynodontidse and Creodonta- 

 Hyjenodontid^e in the upper 

 Oreodon zone. 



FAUXA.*^ 



The rich mammalian fauna 

 (more than 48 species being 

 known in the big badlands of South Dakota alone) is distinguished 

 negatively by the absence of Titanotlierium and positively by the 

 presence of abundant oreodonts. 



The important distinction was first made by Matthew ^ that the 

 Brule clay, or Oreodon zone, of fine, still-water or eohan composition, 



a Dart on, N H., Preliminary report on the geology and undei^ound-water resources of the central 

 Great Plains: Prof Paper U. S Geol Survey No. 32, 1905. 



b Wortman, J L , On the divisions of the White River or lower Miocene of Dakota: Bull. Am. Mus. 

 Nat. Hist , vol. 5, 1S93. pp. 95-105. 



Osbom, H. F . and Wortman, J L , Fossil mammals of the lower Miocene White River beds: Bull. 

 Am. Mus. Nat. Hist , vol 6, 1894, p. 200 (section) . 



c Matthew, W. D., Fossil mammals of the Tertiary of northeastern Colorado: Mem Am. Mus Nat. 

 Hist., vol. 1, pt. 7, 1901, p. 357. 



d See Appendix, p 91. 



e Is the White River Tertiary an eoiian formation? Am. Naturalist, vol. 33, 1899, p. 404. 



Leptauchenia 



cTienia zone Protoceras 

 sandstones " 



Oreodon clays'^ 



Metamynodon 

 sandstones^ 



Titanotherium 

 clays and- 

 zorte sandstones^ 



Fig. 9.— Diagrammatic section of the White River 

 group. South Dakota. (Cf. PI. II. > Chiefly after 

 Wortman. 1892. 



