Proceedings Am. Philosoph. Soc. Vol. XLI. 



Plate X 







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Fig. I. Section of the Leptauchenia volcanic ash beds in a canyon of 

 Sheep Mountain, Big Badlands. The top of the columnar vertical weathering 

 in the picture is the top of division (a) of the Leptauchenia beds, as de- 

 scribed in the text. Above this is the " white ash layer " of Matthew, division 

 {b) of the text. This appears lighter colored than division (a), and does not 

 show vertical columnar weathering. 



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Fig. 2. Section of the Oreodon beds in the Wall of the Badlands at Cedar 

 Pass, north of Interior, Jackson County. The central highest pinnacles are 

 capped by Leptauchenia volcanic ash beds. The subdivision of the Oreodon 

 beds here into upper clays, upper nodular layer, middle clays, and lower nodu- 

 lar layer are clearly shown, especially in the right half of the picture. The 

 upper nodular layer is marked (*) and the lower nodular layer (**). 



