The Arikaree (Miocene) and Ogallala (Pliocene) formations of the North Loup beds are superficial over much of the western half of the state, the former to the N., the latter to the S.
A native plaster is yielded by the Arikaree and Ogallala rocks, but though otherwise of excellent qualities it is ruined by slight exposure to the water.
It is related to the Ogallala beds and occurs only in small areas.
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