84 



CENOZOIC MAMMAL HORIZONS 



the Niobrara River and on the latter." These species were deter- 

 mined by Leidy as follows : ElepJias imperator Leidy, Mastodon mirifi- 

 cus Leidy, Equus excelsus. 



The type of Equus excelsus is elsewhere stated to be from the '^Paw- 

 nee Loup branch of the Platte or Niobrara River." In the same 

 article" a somewhat fuller description of the ^'Loup River beds" 

 makes them include all the deposits down to the top of the White 

 River group, and the faunal list contains several Miocene genera in 

 addition to the more modern types first cited. 



The term ^'Loup River" was again employed by Hay den in 1862, 

 1869 (introduction to Leidy' s memoir), 1871, and 1873. 



It is unfortunate that this upper Pliocene or lower Pleistocene hori- 

 zon, although fairly well defined both geographically and f aunistically, 

 should have been confused by Hay den and Leidy themselves (see 1869, 

 pp. 15-21) with the very much older horizon or true upper Miocene, 

 as part of their Horizon F, including the very rich upper Miocene 

 faunal list. Thus Cope,^ while referring to the very same Nebraska 

 fauna which was described by Leidy " in 1858, applies the terms ^ 'Loup 

 Fork epoch" and ''Loup Fork beds" to the " Santa Fe marls " of New 

 Mexico. The error thus spread into all the subsequent literature. 

 It appears, therefore, that: (1) "Loup River" is the original name. 

 (2) "Loup River" originally included an upper Pliocene or lower 

 Pleistocene horizon. (3) "Loup Fork" is essentially the same name; 

 it is a synonym of "Loup River;" it was defined in still another sense 

 and has been generally used in a very different sense, and must drop 

 out of use entirely. 



PLEISTOCENE. 



VII. SEVENTH FAUNAL PHASE. 



Increasing cold, moisture, and forestation — Third modernization by a grad- 

 ual Eurasiatic invasion of hardy, forest, fluviatile, mountain (alpine), 

 plains, and barren-ground fauna — Gradual extinction of the larger TJngu- 

 lata, of the native North American stocks, of the South American invad- 

 ing stocks, of the Miocene invading Eurasiatic and African stocks. 



LOWER PLEISTOCENE (PREGLACIAL). 



Our knowledge of the mammals in this period is still confined to 

 the western plains and mountains. 



The American Pleistocene begins either with the ElepJias imperator 

 zone (referred above to the upper Pliocene) or with the Equus zone. 

 The exact position of the ElepJias imperator zone, also the question 

 whether it is of the same age as the Equus zone, remain to be deter- 

 mined. In the present review only a few of the characteristic Pleisto- 

 cene deposits will be included, because the subject of Pleistocene cor- 

 relation and succession is in its infancy. 



a Meek and Hayden, Proc. Acad. Nat. Sci. Philadelphia, vol. 13, 1861 (1862), p. 435. 

 h Kept. U. S. Geog. Survey W. 100th Mer. (Wheeler), pt. 2, 1877, pp. 20, 361. 

 c Proc. Acad. Nat. Sci. Philadelphia, 1858, p. 20. 



