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Lakota formation (top only) 
Siltstone, clayey, and hard silty clay- 
stone, light gray, weathers yellowish 
white. With carbonized rootlets and 
irregular branching ferruginous con- 
cretions. 
20. Sandstone, fine-grained, argillaceous, 
gray- white, local purplish streaks. 
Grades into unit below. 
4.4* 
1 . 0 * 
19. Clay stone, silty, tough, locally flinty, 
gray with local orange to red concre- 
tionary masses made up of limonitic 
ooliths of weathered siderite spherulites. 3. 0 1 
18. Claystone, soft, plastic, purple in lower 
part grading up into green gray with 
purpl e mottling. 2.4* 
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