12 THE PLAINS. 



of the bones of animals, the larger of which are generally 

 found in nearly a naturally upright position, as if the 

 animals had mired in the morass. 



On a foundation of stiff clay, or other hard material, 

 a deposit of soft and loose materials, arranged in layers 

 or strata, varying in thickness from thirty to 600 feet, 

 has been made. 



The curious peculiarity of the ' Bad Lands ' formation 

 is, that the channels cut by rains and frost in this soft 

 deposit have almost invariably perpendicular sides, and 

 differ from ordinary ravines in that there is no gradual 

 deepening. They appear to cut at once through the 

 whole thickness of the deposit, are exceedingly tortuous, 

 and vary in width with the nature of the particular 

 locality, or with the length of time that the process of 

 erosion has been going on. 



With this general peculiarity, the 'Bad Lands' vary 

 in the most extraordinary degree. In some localities the 

 upper plain appears at a little distance unmarked ; but an 

 attempt to pass over it discloses the fact that it is scored 

 in every direction by innumerable narrow crooked chan- 

 nels, from thirty to 100 feet in perpendicular depth, 

 and from a few inches to eighty or 100 feet in width. 

 Through such ' bad lands ' no one but the most experi- 

 enced plainsman can hope to make headway. 



In process of time the narrow grass-covered portions 

 of plain between the channels are gradually cut away 

 into backbones, at first very sharp and narrow, getting 

 broader, however, as more of the material is washed 

 away. This is called the ' Hogsback ' Bad Lands, and in 

 most of its stages is utterly impassable. When most of 

 the material inside a particular bed has been washed out, 

 and the Hogsbacks levelled with the foundation plain, the 

 'Bad Lands' present their most striking characteristics. 



Imagine an immense irregular bowl -shaped depression 

 in the earth, from four to ten miles in diameter ; the 

 sides, from 100 to 600 feet high, cut by the action of 



