(4 
174 ANIMALS OF THE PAST 
ment as it was; but when the western moun- 
tains were thrust upward, cutting off the 
moist winds from the Pacific, making great 
changes in the rainfall and climate to the east- 
ward of the Rocky Mountains, these big 
beasts, slow of foot and dull of brain, could 
not keep pace with the change, and their race 
vanished from the face of the earth. ‘The day 
of the little Hyracothere was at the beginning 
of the great series of changes by which the 
lake country of the West, with its marshy 
flats and rank vegetation, became transformed 
into dry uplands sparsely clad with fine 
grasses. On these dry plains the more nimble- 
footed animals would have the advantage in 
the struggle for existence ; and while the four- 
toed foot would keep its owner from sinking” 
in soft ground, he was handicapped when it 
became a question of speed, for not only is a_ 
fleet animal better able to flee from danger 
than his slower fellows, but in time of drouth 
he can cover the greater extent of territory 
in search of food or water. So, too, as the 
rank rushes gave place to fine grasses, often 
; 
horse. They were adapted to their ee 
Sk ait at Ree Se ee 
i el a Sah ae 
sali es 
