PLATE 15 





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Fig. I. Minnekata limestone underlain by Opechee clays, on the railroad in the south limits of Spearfish 

 South Uakota. 1 he clay immediately below the sandstone is deep purple, below it becomes 

 deep red. 



Fig. 2. Minnekata limestone, about one mile south of Beulah. Wyoming, on the banks of Sand Creek. 



