SURFACE. 37 



The prairie dog digs a deep hole with a wide mouth, 

 and piles up around the orifice a mound of earth. It 

 can be seen and avoided in the sharpest chase. The 

 gopher digs a blind pitfall without external opening, and 

 neither man nor horse have any warning of danger. 

 Galloping, or running eager and excited, the horse sud- 

 denly plunges to his knees, turns a somersault, and if 

 both horse and rider regain their feet without a broken 

 bone they are fortunate. 



