Professor Marsh's Monograph of the Dinocerata. 175 
“ This lake-basin, now drained by the Green River, the main 
tributary of the Colorado, slowly filled up with sediment, but 
remained a lake so long that the deposits formed in it, during 
Eocene time, reached a vertical thickness of more than a mile. 
The Wasatch Mountains on the West, and the Uinta chain on 
the South, were the main sources of this sediment, and still 
protect it, but the Wind River range to the North, and other 
mountain elevations, also sent down a vast amount of material 
Into this great fresh-water lake, then more than one hundred 
miles in extent. : 
“At the present time, this ancient lake-basin, now six to eight 
thousand feet above the sea, shows evidence of a vast erosion, 
and probably more than one-half of the deposits once left in it 
ave been washed away, mainly through the Colorado River. 
What remains forms one of the most picturesque regions 1n 
the most fantastic shapes, and varied colors. This same action 
has brought to light the remains of many extinct animals, and 
the bones of the Dinocerata, from their great size, naturally 
first attract the attention of the explorer. 
The first remains of the Dinocerata discovered were found 
” the author, in September, 1870, while cp eeaaies. this 
which had never before been explored. 
n 
secured was the type of Z%noceras tine, described by the 
author in the following year, and now more fully in the present 
Yolume. In the same geological horizon with these remains, 
ri ae and varied vertebrate fauna, hitherto unknown, was 
und. 
“ Among the animals here’represented were ancestral forms 
of the modern horse and tapir, and also of the pig. Many 
others were found related to the recent Lemurs; also various 
Carnivors, Tnsectivors, Rodents, and small Marsupials; and of 
e i 
fat how living. Crocodiles, tortoises, lizards, serpents, an 
fishes also swarmed in and about the waters of this ancient 
lake, while around its borders grew palms, and other tropical 
Vegetation. 
lowin tematic investiga- 
» 8 year, 1871, the author began its systema 
tion, re expedition er i i with an escort = 
Unitea States soldiers, and the work continued during the 
