THE LITTLE MISSOURI BAD LANDS. 471 



brown sandstone, very unequally hardened and mixed with clay. 

 Surmounting the whole is a bed of soft clay of varying thickness, 

 mostly a sort of remnant, persisting only in mounds and the conical 

 heaps already referred to. 



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Fig. 1. Diagrammatic Section of a Single Butte. 



Now, all these strata, except the uppermost sandstone, have this 

 common characteristic : they are composed of particles excessively 

 fine, so that, if from any of the beds a little bit be taken, it may, 

 when dry, be reduced between the fingers to an impalpable powder as 

 fine as ashes. Even the lignite is no exception. If, now, in connec- 

 tion with this fact, and remembering the arrangement of the strata, we 

 take into account the arid climate which prevails in all these regions, 

 we are in position to understand much of the peculiar conformation 

 of the Bad Lands. In the winter the snows are light, and in summer 

 the rain that falls comes in sudden, violent, but short-lived storms. 

 For perhaps half an hour after one of these storms, torrents flood the 

 valleys and low plains between the hills, the rushing waters heavily 

 charged with particles of clay, but particles so fine that they do not 

 readily leave the water or become precipitated, but are borne on to the 

 river, thence to the Missouri proper, which latter stream parts with 

 them only as it blends in the clearer waters of the Mississippi. If, 

 after the storm, we examine again the face of the bluff, we find it 

 striated with numberless tiny channels, down which have just poured 

 little rivulets of water hardly so much as wetting the surface, while 

 from top to bottom the erosion has been about the same, the slightly 

 increased density of the upper layer enabling them to sustain the 

 brunt of the storm, and yet suffer no more wear than the softer strata 

 beneath. 



