290 REPORT OF THE AMERICAN COMMITTEE. 
case only in the Washakie basin, in Wyoming, they are conform- 
able. The Diplacodon beds are, on the contrary, not conformable 
to the Bridger beds, according to King. The relations of the 
Windriver beds to the Wasatch remain undescribed. 
MIOCENE SYSTEM. 
The formations of the Miocene in the interior of North 
A raerica are the following : 
Lonpfork, 
Ticholeptus, 
Johnday, 
Whiteriver. 
These horizons represent succession in time. A formation 
whose relation with the Loupfork epoch is yet uncertain has 
been named " The Dalles." The four series each possess well- 
marked faunas, whose distinguishing features are enumerated 
below. 
Whiteriver. — Mammalia. Presence of a few Lemuroidea (?) 
and Creodonta, Metamynodon (Scott and Osborn), Hyracodon, 
Cryptoproctidse, Poebrotheriidse, Tragulidse, Elotheriidse, and 
Menodontidse. Absence of Felidse, Ursidse, and Rodentia, 
except Sciuridse and Leporidae ; of Camelidse, Equidse, and Pro- 
boscidia. 
There are three areas of this formation. The most extensive 
is the most southern, and occupies a large tract along the White 
River, in Northern Nebraska and Southern Dakota, and ex- 
tends westward into Wyoming and southwestward into North- 
eastern Colorado. The second is much smaller, and is situated 
in Central Dakota, two hundred miles north of the nearest point 
of the southern tract. The northernmost Whiteriver forma- 
tion is in Southern Canada, in the district of Assiniboia, and is 
intermediate in extent between the two previously-mentioned 
areas. Some faunal differences have been noticed between these 
areas, which may be due to geographical distribution, imperfect 
observation, or slight difference of age. Thus, in the Central 
Dakota area, Hysenodon, Hyracodon, and Poebrotherium have 
not yet been found. In the Canadian tract neither of these 
forms has been found, and a genus of Creodonta (Heraipsalo- 
don) is as yet peculiar to it. The thickness of the beds is as 
follows : 
