364 
LOUP FORK EPOCH. 
occurs in the White Eiver beds also; three genera only are common to the 
two beds, as indicated by dental characters of the lower jaw only. 
Dr. Leidy identified this horizon with that of the European Pliocene, 
with reservations expressing doubt as to actual synchronism, and they have 
been so called by subsequent writers. But the omission of the genera 
above enumerated makes an important difibrence, and the additional forms 
discovered have increased the resulting greater antiquity of the facies. 
SteneofiherfoYmerlj referred to the White Riverbeds, probably belongs here. 
The supposed Cervus turns out to be a Dicrocerus of prior geological exist¬ 
ence ; the Mastodon is a near ally of a European species cotemporary with 
the genera mentioned, while one of the Dogs at least is of an ancient t3q3e. In 
view of the entire appropriateness of the association with these of several 
of the genera already known, I remarked* that “the smaller percentage 
of existing genera in the Loup Fork beds, with the persistence of an Oreo- 
dont {Merychyus), indicates that these also should be placed anterior to the 
Pliocene of France”. Still later I referred to them as follows:f—“The facies 
of the fauna of this horizon throughout the West, including, as it does, 
Ampliicyon., Dicrocerus, Hippothermm, AceratJierium (ApJielops), Mastodon^ 
nearly allied to M. angustidens, etc., etc., more nearly resembles the upper 
Miocene of Europe than the Pliocene of that continent.” In confirmation 
of this view, I may take up the genera of the list above given, and shoAv 
their stratigraphic position in Europe:— Pseudceliirus, Miocene, Sansan, Gers ; 
Mustela, Middle Miocene and upward (Broun); Canis, Miocene and 
upward; Ampliicyon, Middle Miocene (Bronn); Dicrocerws, Middle Miocene 
or Helvetien (Renevier); Hippotherium, Middle Miocene and Pliocene; Mas¬ 
todon (type of) angustidens, VppeY Miocene,Tortonien (Renevier); Steneofher, 
Miocene (Bronn). The proper discrimination of the Pliocene fauna of 
North America remains to be accomplished, although Ave are doubtless 
already acquainted with fragments of it. Its existence Avas terminated by 
the Glacial epoch, which separated it from the southern fauna, which occu¬ 
pied the continent after its close. 
A decrease in the abundance of Vertebrate life in North America from 
* Ann. Report U. S. Geol. Sur. Terrs., 1873, p. 4G2. 
t I’roc. Phila. zVcad., J875, p. 257. 
