354 O. C. Marsh— Vertebrate Life in America. 
of Europe, although usually so considered, and known by the 
same names; but, in general, the fauna of ‘each appears to be 
older than that of its corresponding representative in the other 
characteristic genus of which is the ungulate Coryphodon, and 
hence I have called these deposits the Coryphodon Beds. The 
middle Eocene strata, which have been termed the Green 
River and Bridger Series, may be designated as the Dinoceras 
Beds, as the gigantic animals of this order are only found here. 
e uppermost Eocene, or the Uintah Group, is especially 
well apes by large mammals of the genus Diplacodon, 
and hence may be eahed the Diplacodon Beds. The fauna of 
each of these three subdivisions was essentially distinct, and the . 
fossil remains of each were entombed in different and successive 
n 
central plateau of the Continent. As these mountain chains 
were elevated, the enclosed Cretaceous sea, cut off from the | 
drained by the constant deepening of the ries rivers, and 
pe have yerrse remained essentially dry lan 
he Miocene lake-basins are on the wet of this region, 
These basins contain three faunas, nearly or quite distinct. The 
lowest Miocene, which is only found east of the Rocky Moun- 
tains, alone contains the peculiar mammals known as the B Bron- 
totheride, and these deposits may be called the Brontotherium 
Beds. The strata next above, which represent the middle Mio- 
