60 



CENOZOTC MAMMAL HORIZONS 



families — Perissodactyla-Chalicotheriida:', Artiodactyla-Anthracothe- 

 riidse, Siioidea, Creodonta-Hya?nodontida3; (6) first appearance of 

 Carnivora-Mustelidse, probably from the northern continental mass, 

 also Canidae and Felidse-Machaerodontinse; (•7) probable migration 

 to Eurasia of some of the North American families, Perissodactyla- 

 Tapiridse, Amynodontidse. 



LOWER OLIGOCENE, WHITE RIVER GROUP OF HAYDEN (EUROPE, 

 ETAGE SANNOISIEN [TONGRIEN INFERIEUR]). 



7. CHADRON FORMATION ; TITANOTHERIUM ZONE. 



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

 HOMOTAXIS AND SYNONYMY. 



North America. — 1, Horizon A of Hay den and Leidy; lower part 

 of the White River group; 2, Chadron formation, 200 feet, of Bar- 

 ton; 3, Titanotlierium beds" ^ of Leidy and Hay den. South Dakota; 

 4, ''Horsetail Creek beds" of Matthew,^ northeastern Colorado and 

 western Nebraska; 5, Monument Creek formation (upper part) of 

 Darton; 6, White River deposits along Pipestone Creek, Montana 

 (Douglass, 1902); and 7, White River deposits along Swift Current 

 Creek, Cypress Hills, British Columbia,^ etc. 



Europe, provisional Jiomotaxis. — Ludien, in part; Sannoisien (Ton- 

 grien inferieur); Stampien (Tongrien superieur). 



FAUN A. ^ 



It is important to note again that four or more of the newly 

 appearing families of mammals are represented in the upper Eocene 

 of Europe. Our knowledge of the animals of this stage, which is at 

 ]:)resent considered lower Oligocene, is still rather limited except as to 

 the Titanotheriidse, which are very abundant and characteristic. In 

 the White River beds at Pipestone Springs, Montana,^ were first dis- 

 covered (Douglass^) the animals of smaller size or microfauna. In 

 all the other deposits chiefly the larger animals are known. 



o Hatcher, J. B., The Titanotherium beds: Am. Naturalist, Mar. 1, 1893, pp. 204-221. 



& Matthew, W. D., Stratigraphy of the White River and Loup Fork formations: Bull. Am. Mus. 

 Nat. Ilist., vol.1, pt. 7, 1901, pp. 355-374. 



<;Cope, E. D., The White River beds of Swift Current River, Northwest Territory (Geol. Oligocene 

 White River): Am. Naturahst, Feb., 1885. Also Ann. Rept. Geol. and Nat. Hist. Survey Canada, 

 vol. 1, 1885 (1886), appendix to Article C, pp. 79-85. 



d See Appendix, p. 91. 



Scott, W. B., and Osborn, H. F., Preliminary account of the fossil mammals from the White River 

 formation contained in the Museum of Comparative Zoology: Bull. Mus. Comp. Zool. Harvard Coll., 

 vol, 13, 1887, pp. 151-171. 



Osborn, H. F., and Wortman, J. L., Fossil mammals of the lower Miocene White River beds, coll. 

 1892: Bull. Am. Mus. Nat. Hist., vol. 6, 1894, pp. 199-228. 



c Matthew, W^D., The fauna of the Titanotherium beds of Pipestone Springs, Montana: Bull. Am. 

 Mus. Nat. Hist., vol. 19, 1903, pp. 197-22G. 



/Douglass, Earl, New vertebrates from the Montana Tertiary: Ann. Carnegie Mus., vol.2, No. 2, 

 1903, pp. 145-200. (White River stratigraphy.) 



