286 REPORT OF THE AMERICAN COMMITTEE. 
nary, since it implies what appears to me to be an erroneous 
classification. This classification makes the formations in ques- 
tion one of four primary divisions of geological time. To this 
position I cannot perceive that it is entitled on the evidence, 
which rather shows that it forms one of the systems of Ceno- 
zoic time. I use for it, therefore, the term Plistocene, and include 
in it all formations from tlie commencement of the drift to the 
most modern deposits inclusive. 
The characteristic features of the faunas of these divisions are 
as follows : 
Eocene. — Mammalia. Presence of Tillodontia, Tceniodontia, 
Mesonychidse, Amblypoda, Condylarthra, and Lophiodontidee. 
Absence of Carnivora,* R.uminantia,f Proboscidia, Leporidse, 
and Anthroporaorpha (Europe). Pisces. Presence of Osteo- 
glossidse and Gonorhynchidee. 
Miocene. — Mammalia. Presence of Carnivora, of E,hinoce- 
rontidse, Leporidse, Ruminantia,* and of Edentata. Absence of 
Tillodonta, Tpeniodonta, Amblypoda, and Condylarthra. 
Pliocene. — Presence of extinct families of Mammalia : Casto- 
roididaj, Glyptodontidse, Megatheriidse, and Eschatiidse, and of 
extinct genera, as Ilolomeniscus and Hippotherium. 
Plistocene. — Mammalia. All families are recent and most 
of the genera ; many species also recent. 
Lithologically speaking, the Cenozoic formations of the inte- 
rior of North America are much alike. They consist from the 
base of the Eocene to the base of the drift, exclusive of the latter, 
of layers of more or less calcareous, and more or less arenaceous, 
clay marls, interstratified with beds of impure and rarely hard 
sandstone. The arenaceous character increases with the lapse of 
time, so that the Ticholeptus Miocene is partly sandy, and the 
Loupfork Miocene consists almost exclusively of calcareo- 
arenaceons beds, alternating with nearly pure sandstones of vary- 
ing, sometimes considerable, hardness. A hard sandstone is found 
in the Whileriver Miocene. Of course the beds have the char- 
acter of the shores of the basins in which they were deposited. 
Thus the material of the Johnday Miocene is shown by King 
to consist of the disintegrated volcanic ejecta of which the sur- 
* One genus in the Diplacodon beds. 
t I.e., quadritiiherciilar Selenodont Artiodactyla. Two genera ai-e found in 
the Diplacodon beds. 
