OF WESTERN NOKTIL AMERICA. 



78 



WESTERLY SECTION. 

 (Figs. 13, 14.) 



The recognition of this fauna ^ is the most important advance of 

 recent mammaUan paleontology in North America. As ffybserved 

 by Peterson,^ continuing the observations of Hatcher/ in a sec- 

 tion run through northwestern Nebraska and southeastern Wyo- 

 ming, we find three distinct formations, as described below. 



A. LOWER DIVISION. 



(a) Gering formation {or lower part of Monroe Creelc). — Among 

 Artiodactyla-Oreodontidse, Mesoreodon, Leytauchenia. The species 

 of LeptaucJienia are but slightly more progressive than those {L. 

 decora, L. nitida) of the underlying Leptauchenia zone or upper part 

 of the Brule clay. 



Q)) Monroe CreeTc formation. — Among Artiodactyla-Oreodontidse, 

 Mesoreodon, PromerycocJioerus, Phenacocoslus; among Camelidse, 



BRULE 



Fig. 14. — Diagrammatic section of the Gering, Monroe Creek, and Harrison formations of western 

 Nebraska. Modified from Peterson, 1906. For the line of this section see section A, PI. II. 



Protomeryx; among Rodentia, Euhapsis platyceps; among Canidse, 

 Nothocyon; among Rhinocerotidae, Dicer atlierium. 



(c) Harrison formation, H atelier. — These are the "Ddemonelix 

 beds" of Barbour. The great spirals or corkscrews to which the 

 name Dsemonelix was applied are found to contain remains of the 

 characteristic lower Miocene rodents, CsLstoridse-Steneofiher (an 

 aberrant castoroid), and are believed by Peterson^ to represent the 

 burrows of this rodent. The original theory of Barbour (1892) 

 was that these corkscrews represent the spiral roots of some giant 

 plant. Neither theory is entirely satisfactory. The Harrison forma- 



o See Appendix, p. 91. 



h The Miocene beds, etc.: Ann. Carnegie Mus., vol. 4, 1906, p. 23. 



c Origin of the Oligocene and Miocene deposits of the Great Plains: Proc. Am. Philos. Soc, vol. 41, 

 1902, pp. 118-119. 

 d Mem. Carnegie Mus., vol. 2, 1905, pp. 139-191. 



