368 THE AGE OF MAMMALS 



that older and newer mammals are intermingled in these collections. The 

 greatest anachronism is the reported occurrence of Bison. He states that 

 the following fossils were collected in Peace Creek at Arcadia, Florida, 

 from a sand bar which is exposed when the water is low: Tapirus, a tapir 

 resembling the T. americanus of South America; a true horse, Equus; teeth 

 and bones which may belong to some extinct species of Hipparion, a 

 small three-toed equine; Bison, of the size of the recent American bison; 

 a deer similar to the recent Odocoileus; a mammoth provisionally referred 

 to E. columbi; among edentates, a glyptodont probably similar to Glypto- 

 therium, also Megalonyx. The Sirenia appear in the manatee (Manatus). 

 Among the reptiles there is a gigantic species of land tortoise (Testudo 

 crassiscutata) as well as trionychids and emyids. Among the Proboscidea 

 is recorded the true mastodon, M. americanus. 



It seems hardly possible that this assemblage is all of the same age, 

 and careful stratigraphic work and more accurate systematic determination 

 of the species of mammals are necessary before the Upper Pliocene age of 

 these forms can be considered as proved. The conclusion, however, seems 

 well founded that we have here an Equus, Elephas, Glyptotherium fauna 

 either of very late Pliocene or of early Pleistocene age. 



' Loup River,' Nebraska, Formation, 

 Elephas Imperator Zone 



The same uncertainty applies as to the Upper Pliocene age of the original 

 'Loup River' formation described by Meek and Hayden in 1861-1862 

 in Nebraska, and to certain formations as yet unnamed in Texas and 

 Mexico, which also contain remains of Equus and of Elephas imperator. 



The typical 'Loup River' beds were first characterized by Meek and 

 Hayden^ as follows: "Fine loose sand with some layers of limestone — 

 contains bones of Canis, Felis, Castor, Equus, Mas odon, Testudo, etc., 

 some of which are scarcely distinguishable from living species." These 

 sands lie on the Loup River or Loup Fork of the Platte River. Of the 

 bones collected in this locality Leidy observed in 1869: "Other remains 

 of elephants, as Dr. Hayden supposed them to be, he observed in association 

 with those of Mastodon mirificus, Equus excelsus, and Hipparion at the 

 head of the Loup Fork branch of the Platte River; also between this point 

 and Niobrara River and on the latter." These species were determined by 

 Leidy as follows: Elephas imperator, Mastodon mirificus, Equus excelsus. 



The term Loup River, which was thus very loosely defined and cir- 

 cumscribed at the outset, together with the animals which it contained, 

 although employed by Hayden in 1862 and 1869,- in 1871 and 1873, was, 



' Proc. Acad. Nat. Sci. Phila., Vol. XIII, 1861 (1862), p. 433. Also Leidy, J., Extinct 

 Mammalian Fauna of Dakota and Nebraska, 1869, p. 255. 

 ^ See Leidy, op. cil., 1869, Introduction. 



