1887] Mesozoic and Cenozoic of North America. 45> 
species of Oreodontidz, and in the absence of Cosoryx. Th 
formation is known from three regions: first, from Western Ne. 
braska; second, from the valley of Deep River, Montana; anq 
third, from Cottonwood Creek, Oregon. Its thickness has not 
yet been stated. 
Loup Forx.—Mammalia. Presence of Felidae, Camelida 
Equide, Proboscidia, Cosoryx, Glyptodontidz, and Hystriciday, 
Absence of Tragulidz, Oreodontidz (with very few exceptions), 
Poébrotheriide, Elotheriidz, and Nimravide. 
This formation has a wide extent throughout North America, 
The largest area overlies the White River® beds in Nebraska, 
Wyoming, and Colorado,” extending south and east of that for. 
mation into Kansas, where it rests on the Cretaceous. There iş 
a second area in Northern Central New Mexico, and one per. 
haps in Southern New Mexico, extending from the Rio Grandę 
to near the Arizona border.s There is another tract in Wash. 
ington County, Texas ; and yet another in Mexico, on the bound, 
aries of the states of Hidalgo and Vera Cruz.% According to 
King its thickness in Wyoming reaches two thousand feet, but 
it thins out gradually to the eastward, so as to have a thickness 
on the White River of about one hundred and fifty feet, accord. 
ing to Hayden. 
This formation was referred to the Pliocene series by King anq 
Hayden, and I have called it Upper Miocene. The latter view 
is supported by the presence of the following European Mioceng 
genera and species: Cosoryx, Paleomeryx (= Blastomeryx); 
Castor div. Steneofiber; Mastodon (Tetrabelodon) angustidens, 
The remaining Oreodontide (Merychyus) give it a facies older 
than Pliocene. 
This series has received the name of Niobrara® from Marsh, 
a term previously applied to a division of the Cretacic. It in, 
cludes the Humboldt,” and probably the North Park formations 
of King.® 
PLIOCENE. 
Under this head I include everything between the Miocene anq 
the glacial epoch. It includes the following divisions. Two of 
them are consecutive in time, viz. : 
Equus beds, 
Idaho. 
VOL. XXIL—NO. 5. 31 
